The Texans are optimistic Watt will be ready to play at the start of the regular season. But sources told ESPN's Tania Ganguli there was concern his availability for the early part of the season could be compromised.
Watt, who has never missed a regular-season game, will open training camp on the physically unable to perform list and will miss the preseason, the sources said. He didn't play during last year's preseason to preserve his health.
The Houston Chronicle previously reported Watt's back surgery.
Watt played last season with a herniated disk in his back, and sources told Ganguli that Watt had surgery for the same issue. Watt also had a broken hand and five torn muscles in his core area last season. He had a major surgery to repair the muscles after last season ended and had been rehabbing that. Some of the tears happened early in the season.
He reached a breaking point with the torn muscles during the Texans' wild-card playoff game against the Kansas City Chiefs. In the third quarter, the Texans pulled Watt. Despite his protests, team trainer Geoff Kaplan did not allow him back in the game.
Even amid that turmoil, Watt won his third defensive player of the year award for his 17.5-sack 2015 season.
Information from ESPN's Adam Schefter was used in this report.