Williams said in the locker room Monday that the operation in Alabama was done to "clean up" his wrist and he can already detect better range of motion in his left hand.
Williams was absent last week because of the injury, which has been bothering him since the final week of the preseason. It's unclear when the Bills learned Williams was going ahead with his treatment.
The Bills made Williams the NFL's highest-paid defensive player by signing him to a six-year, $100 million contract in March.
Williams has been looking forward to playing against his former team, the Texans (6-1). This game, however, comes as he has taken the brunt of criticism for Buffalo's underperforming defense.
Buffalo (3-4) has allowed an NFL-worst 1,238 yards rushing - that's 986 yards short of the team's total last season - and that includes giving up a combined 937 yards rushing in its last four games.
Williams is a two-time Pro Bowl selection who in six seasons in Houston set the Texans franchise record with 53 sacks.
In Buffalo, he's second on the team with 3 1/2 sacks. That's down from last year in Houston, where he had five sacks in five games before landing on the season-ending injured reserve list because of a chest injury.
"I'm hesitant," he said earlier this month. "I don't know if it's just me in general, but that's on me and that's fine. I know I have to change that, believe me. I don't need anybody to tell me that. I look at it just like everybody else does."
Williams' injury has proved costly for the Bills. The NFL fined Buffalo $20,000 on Friday, by ruling that Williams should have been on the team's injury report since the start of the season even though he had not missed a practice.