Jets coach Rex Ryan said Thursday that Sanchez's sore shoulder is worse than he first thought, though he still expects the quarterback to start Sunday at Chicago. If not, 40-year-old Mark Brunell would be under center.
"This one could be more of a game-time type decision than I thought it would be," Ryan said.
Sanchez was limited in practice for the second consecutive day and "never had a ton of zip" on his passes, according to Ryan. But offensive coordinator Brian Schottenheimer saw it differently, offering a more optimistic evaluation.
"As he got going a little bit, he looked pretty good," Schottenheimer said. "Early in the day, Mark was trying to get loose. He had an 18-yard curl route that was awfully sharp."
Ryan wouldn't confirm published reports that an MRI exam Monday revealed a slight cartilage tear in Sanchez's shoulder, hurt during New York's second drive in last Sunday's 22-17 win at Pittsburgh.
NFL Network insider Albert Breer confirmed the report Wednesday through a league source.
Sanchez finished the game and played well through the injury. He was 19-of-29 passing for 170 yards and ran for a touchdown, stopping an eight-game interception streak.
"I still think he's going to play, but I was shocked a little bit," Ryan said. "The fact that he played the game and he looked great, I think I made an assumption that maybe I shouldn't have."
Earlier in the week, Ryan said he was 99 percent sure that Sanchez would play. The coach downgraded that number to 80 percent Thursday.
Sanchez wasn't available to the media because he talks on Wednesdays, but he has said he's "playing, that's all there is to it."
Ryan said the decision whether or not Sanchez plays will be made by the team, along with input from the quarterback. The coach said he made a mistake earlier this season when he allowed cornerback Darrelle Revis to decide if he was ready to return from a tweaked hamstring, and it worsened.
Sanchez threw more passes during practice Thursday than he did Wednesday, an encouraging sign. Both Ryan and Schottenheimer believe the decision likely will come down to Sanchez's threshold for pain, but the team won't put him in if he can't perform.
"He's still got to improve before we'll be comfortable with him out there as our starting quarterback," Ryan said. "Do we think he will? Yes, we do think he'll be better. This is what I've said the whole time about it being a sore shoulder."
Brunell, signed during the offseason after two years with the New Orleans Saints, is prepared to step in for Sanchez if needed. Brunell's last start came in the regular-season finale last year as Drew Brees rested for the Saints' eventual Super Bowl-winning push.
"You have to be ready, that's the job of a backup," Brunell said.
Schottenheimer said the Jets wouldn't have to change much of their offensive game plan if Brunell starts, except for the fact he's left-handed.
"There'd be a few things here or there you might want to flip over and run the other way," Schottenheimer said. "For the most part, you don't change too much."
"He's smart, he's done it all," Ryan said of the 18-year veteran. "We're not talking about a guy who's never done it before in his career. This guy was a Pro Bowl quarterback for a number of years. Is he as good as Mark Brunell was back then? No, because he'd be our starting quarterback. I feel comfortable with Mark, I really do."
Notes: Safety Eric Smith (concussion) was ruled out for the second consecutive game, as was RT Damien Woody (right knee). ... WR Santonio Holmes (turf toe) was limited in practice, but Ryan expects him to play Sunday.
The Associated Press contributed to this report.