"We did try to exhaust all the non-surgical remedies. Jay is a tough guy and proved that to me in the past," Fox said. "We did multiple different types of rehab. It's been a couple weeks now. Now the next alternative is to have surgery. He'll have surgery on Saturday."
Cutler, 33, suffered the tear in Chicago's loss at New York on Nov. 20 but finished the game.
Fox initially described the injury as "day to day."
"He's tough and waited the weeks doing a lot of rehab," Fox said. "They are in there doing rehab at all hours of the day. There were some different treatments -- I'm not going to get into all the specifics -- but he did things you do to try and avoid surgery. They didn't take form like they were expecting, and we're at the surgical mode at this point."
Cutler's future in Chicago is in question. Since the guaranteed portion of Cutler's contract runs out after 2016, the Bears would take a $2 million cap hit if they trade or release Cutler in the offseason, but the move would open up $13 million worth of space.
Fox refused to discuss Cutler's long-term status.
"Right now we have five games left and all of our focus is on San Francisco," Fox said. "The offseason is the offseason. We are not there yet."
Cutler is 51-51 with the Bears since he arrived in 2009 from the Denver Broncos. During that span, Cutler ranks 26th in the NFL in Total QBR, 25th in completion percentage, 27th in yards per attempt and 35th in touchdown to interception ratio -- among 47 qualifying quarterbacks. Cutler led the Bears to one playoff berth in 2010.
Cutler posted a career-high 92.3 quarterback rating under former coordinator Adam Gase last season, but he appeared in only five games in 2016.
Aside from the torn labrum, Cutler missed five games because of a thumb injury. He finishes the year with four touchdowns and five interceptions (78.1 passer rating). Cutler also lost two fumbles.
Still, Cutler's current playcaller, Dowell Loggains, said he learned a lot about the embattled quarterback.
"Just how tough he is," Loggains said. "How much he cares. How much the team means to him. That's been incredible to watch. There is a perception, and then there is a reality of that. It's been really fun the last two years being able to coach him. I've enjoyed every minute of it."