Cassel was back on the practice field in Kansas City, one week after undergoing an appendectomy that kept him out of last Sunday's loss at San Diego, but whether or not he will start Sunday against the St. Louis Rams remained uncertain.
Cassel worked in non-contract drills Wednesday, handing off to running backs Jamaal Charles and Thomas Jones, and completed 40-yard passes to wide receivers Terrence Cooper and rookie Verran Tucker in a brief period when practice was open to the media.
"I don't think there is anyway to predict how he is going to move through the week. He was out there (Wednesday) in a limited capacity. It's not your normal injury situation that you normally deal with. There are a lot of factors in play."
Cassel smiled and said, "hopefully, 99.999 percent" he would play Sunday at St. Louis.
"I really don't know," Cassel said. "Right now, I think we're day to day. The medical staff, the trainers will discuss it, and we'll proceed with caution and see where I'm at.
"I think medically there are a number of different issues that come up with a procedure like this in terms of just how I feel. If I can go out there and do everything I want to do without any discomfort, without any pain then I'm going to go out and play."
Cassel said he took "a lot of snaps" in practice.
Cassel has completed 59.9 percent of his passes this season with 23 touchdowns and just four interceptions. With Cassel out at San Diego last weekend, the Chiefs' offense staggered with Brodie Croyle at quarterback. The Chiefs lost 31-0 with the offense managing just 67 yards, five first downs and a woeful 0-for-11 on third-down conversions.
"It wasn't what we expected," Croyle said Wednesday. "It wasn't what I expected. We fully thought we were going to go out there and run the game plan the way it was supposed to be executed, and we didn't do it. We didn't score points. It's disappointing, but we're moving on. We still have three games to go."
"I'm fine," Croyle said. "I've been around long enough to know it's not always going to go your way. You just have to regroup and get ready for the next week. That's the great part about pro football: There's always another week."
If Cassel plays, he could wear a protective jacket.
"If they recommend that, that's something we'll definitely try to use during practice, so you just get a feel for it," Cassel said.
When Cassel came in last Wednesday with abdomen pain, he didn't believe it was serious.
"I really didn't know what an appendix was until they told me," he said. "I thought I was going to come in and take some Pepto-Bismol and we were going to run. Unfortunately, it was a little more severe than that. I feel like a new man with it out."
Kansas City (8-5) has a one-game lead over San Diego (7-6) in the AFC West with three games remaining, all against sub-.500 teams. The Chiefs have lost five of seven road games, and St. Louis (4-2 at home) is their final away game.
"We're in a tight division race and we know that," Cassel said. "We know the games continue to get bigger and bigger in each of these games in December."
The Associated Press contributed to this report.