13D Filing: Discovery Group I, LLC and Entellus Medical Inc (ENTL)

UNITED
STATES

SECURITIES
AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

(Rule 13d-101)

INFORMATION TO BE INCLUDED
IN STATEMENTS FILED PURSUANT

TO § 240.13d-1(a) AND
AMENDMENTS THERETO FILED

PURSUANT TO § 240.13d-2(a)

UNDER THE SECURITIES EXCHANGE
ACT OF 1934

(Amendment No. 4)*

Entellus
Medical, Inc.

(Name of Issuer)

Common Stock, par value
$0.001 per share

(Title of Class of Securities)

29363K105

(CUSIP Number)

Discovery Group I, LLC

300 South Wacker Drive

Suite 600

Chicago, Illinois 60606

Telephone Number: (312)
265-9600

(Name, Address and Telephone
Number of Person

Authorized to Receive Notices
and Communications)

August 21, 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 §§240.13d-1(e), 240.13d-1(f) or 240.13d-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 §240.13d-7 for
other parties to whom copies are to be sent.

^*The remainder of
this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of
securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

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).