Cassel, who injured his left knee in a preseason game Aug. 29 and sat out the season opener at Baltimore, is starting at quarterback against the Oakland Raiders on Sunday.
Cassel's left knee was still braced this week in practice, but the slight limp he had last week was not evident.
Cassel signed a six-year contract for a guaranteed $28 million after coming from New England in a trade.
Brodie Croyle started in Cassel's place in the 38-24 loss to the Ravens and hit 16 of 24 passes for 177 yards and two touchdowns.
Information from ESPN's Adam Schefter and The Associated Press was used in this report.