Texans All-Pro defensive end J.J. Watt underwent back surgery Thursday and will begin training camp on the physically unable to perform list, as first reported by Houston Chronicle.

Watt has spent much of the offseason recovering from an especially taxing 2015, in which he suffered at least five partially or fully torn muscles in his torso, groin and upper legs. He underwent surgery in January to repair a sports hernia in his groin region. He also broke his hand last season and said he played with a herniated disk.

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The nature of Watt's most recent surgical procedure wasn't immediately clear, but he's expected to be ready for Houston's Sept. 11 regular-season opener.

The three-time NFL Defensive Player of the Year has not missed a game in his five-year pro career. He has twice led the league in sacks, including with 17.5 last season, and has 74.5 in his 80 starts.

The Texans open training camp Aug. 1.