Collins, a third-year pro, injured his left knee midway through the third quarter while tackling Chiefs receiver Samie Parker. Collins was taken to the locker room for X-rays and did not return.
Rouse filled in for Collins and played well, McCarthy said.
"I thought Aaron played solid," McCarthy said. I thought he graded out in a positive light. If he has to go, I feel very confident, just like we played when Nick went down. We'll be fine."
Rouse has seen limited playing time this season behind Collins. He played a handful of snaps Sept. 30 against Minnesota when Atari Bigby had to leave the game with an injury. Rouse also has been active on a number of special teams units.
Rouse missed the Packers' final preseason game and the first three games of the regular season with a hamstring injury. He had three tackles against the Chiefs on Sunday. He assisted on one tackle from scrimmage entering the game.
"He's very bright," McCarthy said. "If you go back to the OTA's (Organized Team Activities) practices, he picked up the defense very quickly. It's his opportunity. A lot of young players get their opportunity this way. I'm not concerned about him. You never know until they play in a real game, and it's his time."
Running back Ryan Grant did not play in Green Bay's final series of the game after sustaining a concussion. Grant, who rushed for a career-high 104 yards against Denver, finished with 55 yards on 19 carries (2.9 avg.) against he Chiefs. He was replaced by Brandon Jackson.
Grant's status for this Sunday's game against Minnesota is uncertain.
Linebacker/special teams specialist Tracy White sustained a sprained ankle, and defensive tackle Ryan Pickett injured his knee, but is expected to play against the Vikings. White's status is uncertain.