McIlroy finished with bogeys on hole Nos. 6 and 9 on Friday to drop to 1-under par after two rounds at the FedEx St. Jude Championship.
The cut is the top 65 and ties after 36 holes. As of 2 p.m., 69 players are at 2-under or better.
This week was McIlroy's first tournament since The Open Championship in July, where he fell short in winning his first major championship since 2014 despite leading on Sunday.
If McIlroy does the miss the cut, it would be his second missed cut of the season and his first since the Valero Texas Open in April.
McIlroy shot even-par 70 on Thursday, and had a solid round going on Friday after birdies on hole Nos. 1 and 2 following a bogey on No. 18 after his tee shot found the water.
But a wayward tee shot short and left on No.. 6 forced McIlroy to lay up, and a par putt from 16 feet slid past the hole.
On hole No. 9, McIlroy's tee shot went into the right rough. His approach went well past the green, and he could only manage a lengthy par putt that fell short.
This article originally appeared on Memphis Commercial Appeal: Rory McIlroy in danger of missing cut at FedEx St. Jude Championship