Trevathan becomes the 15th Bears player to land on injured reserve in 2016.
"He's obviously a very talented player and a guy we targeted and went after in the offseason," coach John Fox said Monday. "Unfortunately, he also had a thumb injury that required surgery earlier in the season [forcing him to miss two weeks]. But he looked very good in the offseason work and in training camp.
"This was a semicontact injury behind the ball. He planted wrong, and the injury occurred."
At the 2:52 mark of the fourth quarter, Trevathan charged into the backfield to tackle Titans running back Derrick Henry, but the linebacker's knee appeared to buckle. Trevathan stayed on the ground for over a minute until medical personnel helped him slowly walk off the field.
"He'll fight back," Fox said. "He's been through this before. He had a similar injury [in Denver in 2014] that he worked through, and he'll do the same off of this one."
Trevathan's injury could affect his 2017 playing status. Patellar tendon tears typically require six to nine months before resuming sports activities, but some players take up to a full year to return to form, according to ESPN injury analyst Stephania Bell.
One of Chicago's team leaders on defense, Trevathan signed a four-year contract in the offseason that contained $12 million in guaranteed money. He is scheduled to count for $3.35 million against the Bears' salary cap in 2017.
Before joining the Bears, Trevathan played four years in Denver, where he helped the Broncos win Super Bowl 50.
The Bears are expected to replace Trevathan with second-year linebacker John Timu. Rookie fourth-round pick Nick Kwiatkoski started at the other inside linebacker spot Sunday in place of veteran Jerrell Freeman, who is serving a four-game suspension for violating the NFL's policy on performance-enhancing substances.