13D Filing: Red Mountain Capital and Destination Xl Group Inc. (DXLG)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE
13D/A

Under the Securities Exchange Act of 1934

(Amendment No. 6)*

DESTINATION
XL GROUP, INC.

(Name of Issuer)

Common Stock, $0.01 par value

(Title of Class of Securities)

25065K104

(CUSIP Number)

Red Mountain Capital Partners LLC

Attn: Willem Mesdag

10100 Santa Monica Boulevard, Suite 925

Los Angeles, California 90067

Telephone (310) 432-0200

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

May 19, 2017

(Date
of Event Which Requires Filing of this Statement)

If the filing person has
previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of Rule 13d-1(e),
13d-1(f) or 13d-1(g), check the following box.  ☐

Note. Schedules filed in paper format shall
include a signed original and five copies of the schedule, including all exhibits. See Rule 13d-7 for other parties to whom copies are to be sent.

The information required on the remainder of this cover page
shall not be deemed to be filed for the purpose of Section 18 of the Securities Exchange Act of 1934 (Act) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the
Act (however, see the Notes).

* See Instructions

* See Instructions

* See Instructions

* See Instructions

* See Instructions

This Amendment No. 6 amends and supplements the Schedule 13D filed with the Securities
and Exchange Commission (the SEC) on March 25, 2013, as amended by Amendment No. 1 thereto, filed with the SEC on October 10, 2013, Amendment No. 2 thereto, filed with the SEC on December 16, 2013, Amendment
No. 3 thereto, filed with the SEC on January 31, 2014, Amendment No. 4 thereto, filed with the SEC on March 24, 2014, and Amendment No. 5 thereto, filed with the SEC on April 2, 2014, in each case by (i) Red
Mountain Capital Partners LLC, a Delaware limited liability company (RMCP LLC), (ii) Red Mountain Partners, L.P., a Delaware limited partnership (RMP), (iii) RMCP GP LLC, a Delaware limited liability company (RMCP
GP), (iv) Red Mountain Capital Management, Inc., a Delaware corporation (RMCM), and (v) Willem Mesdag, a natural person and citizen of the United States of America, with respect to the common stock, par value $0.01 per share
(the Common Stock), of Destination XL Group, Inc., a Delaware corporation (Destination XL). The filing of any amendment to this Schedule 13D (including the filing of this Amendment No. 6) shall not be construed to be an
admission by the Reporting Persons (as defined below) that a material change has occurred in the facts set forth in this Schedule 13D or that such amendment is required under Rule 13d-2 of the Securities
Exchange Act of 1934, as amended.

RMCP LLC, RMP, and RMCP GP are sometimes collectively referred to herein as Red Mountain.
Red Mountain, RMCM and Mr. Mesdag are sometimes collectively referred to herein as the Reporting Persons.

The Reporting
Persons are filing this Amendment No. 6 as a result of a reduction in the number of shares of Common Stock outstanding, as reported by Destination XL in their quarterly periodic filing with the Securities and Exchange Commission filed on
May 19, 2017.

ITEM 3. SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION.

Item 3 of this Schedule 13D is hereby amended to include the following information:

Between February 1, 2016 and May 31, 2017, Destination XL issued 34,174 shares of deferred stock (Deferred Stock) to
Mr. Mesdag in connection with his service on the board of directors of Destination XL (the Board). Each share of Deferred Stock is the economic equivalent of one share of common stock. The shares of Deferred Stock become payable in
Common Stock within 30 calendar days after the date Mr. Mesdag ceases to be a director on the Board.

Between February 2, 2015
and January 29, 2016, RMCP LLC received 22,771 shares of Common Stock issued by Destination XL in connection with Mr. Mesdags service on the Board.

Between August 29, 2016 and January 13, 2017, RMCP LLC purchased an aggregate of 302,344 shares of Common Stock on the open market
for an aggregate purchase price (excluding trading commissions and related administrative costs) of $1,268,998. The source of the funds used by RMCP LLC to purchase such shares was working capital of RMCP LLC.

ITEM 5. INTEREST IN SECURITIES OF THE ISSUER.

Items 5(a) and 5(b) of this Schedule 13D are hereby amended and restated as follows:

Because RMCP GP may be deemed to control RMP, RMCP GP may be deemed to beneficially own, and
to have the power to vote or direct the vote of, and the sole power to dispose or direct the disposition of, 7,522,354 shares of Common Stock, representing approximately 15.2% of the outstanding Common Stock.

RMCP LLC beneficially owns directly 325,115 shares of Common Stock, which represent approximately 0.7% of the outstanding Common Stock. RMCP
LLC has the sole power to vote or direct the vote, and the sole power to dispose or direct the disposition, of all such 325,115 shares of Common Stock. In addition, because RMCP LLC may be deemed to control RMCP GP and RMP, RMCP LLC may be deemed to
beneficially own, and to have the power to vote or direct the vote of, or dispose or direct the disposition of, all of the Common Stock beneficially owned by RMCP GP and RMP. As a result, RMCP LLC may be deemed to beneficially own, in the aggregate,
7,847,469 shares of Common Stock, representing approximately 15.8% of the outstanding Common Stock.

Because each of RMCM and
Mr. Mesdag may be deemed to control RMP, RMCP GP and RMCP LLC, RMCM and Mr. Mesdag may be deemed to beneficially own, and to have the power to vote or direct the vote of, or dispose or direct the disposition of, all of the Common Stock
beneficially owned by RMP, RMCP GP and RMCP LLC. Therefore, each of Mr. Mesdag and RMCM may be deemed to beneficially own, in the aggregate, 7,847,469 shares of Common Stock, which represent approximately 15.8% of the outstanding Common Stock.

In addition to any shares of Common Stock beneficially owned directly by RMP and RMCP LLC, Mr. Mesdag may be deemed to own the 15,000
shares of Common Stock receivable upon exercise of the Director Options, all of which are currently exercisable, as well as the 34,174 shares of Common Stock receivable upon settlement of the Deferred Stock as a result of a separation of service
from the Board. As a result, Mr. Mesdag may be deemed to beneficially own, in the aggregate, 7,896,643 shares of Common Stock, which represent approximately 15.9% of the outstanding Common Stock.

Each of RMCP LLC, RMP and RMCP GP affirms membership in a group with each other but disclaims membership in a group with RMCM or
Mr. Mesdag. Each of RMCM and Mr. Mesdag disclaims membership in a group with any person.

The filing of this Schedule 13D shall
not be construed as an admission that any Reporting Person is the beneficial owner of any of the shares of Common Stock that such Reporting Person may be deemed to beneficially own. Without limiting the foregoing sentence, each of RMCM and
Mr. Mesdag disclaims beneficial ownership of all shares of Common Stock reported as beneficially owned by RMP or RMCP LLC in this Schedule 13D, and RMCM disclaims beneficial ownership of all shares of Common Stock reported in this Schedule 13D.
In addition, the filing of this Schedule 13D shall not be construed as an admission that any partner, member, director, officer or affiliate of any Reporting Person is the beneficial owner of any of the shares of Common Stock that such partner,
member, director, officer or affiliate may be deemed to beneficially own. Without limiting the foregoing sentence, Mr. Teets disclaims beneficial ownership of all shares of Common Stock reported in this Schedule 13D.

Item 5(c) of this Schedule 13D is hereby amended to include the following information:

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true,
complete and correct.

Dated: June 13, 2017

EXHIBIT INDEX