Thomas, 31, suffered a season-ending torn Achilles in December. He was due a non-guaranteed $14 million salary in 2019.
He said he was not thinking about retiring.
"My main priority right now is getting back healthy. I can still play, man. I'm not thinking about retirement. I just don't know where it will be," he told reporters, according to the Houston Chronicle.
Thomas was acquired by the Texans from the Denver Broncos before last year's trading deadline. The four-time Pro Bowl selection caught 23 passes for 275 yards and two touchdowns in seven games after the trade.