There doesn't appear to be a fracture, but the QB will have an MRI on Friday to determine whether he suffered any ligament damage, Palmer adds.
If no ligament damage is found, Mahomes' best-case scenario would be a three-week layoff, a source told ESPN's Adam Schefter.
A cart initially came onto the field but the star passer waved it off and limped to the sideline with some assistance. He quickly headed to the locker room to undergo additional tests and was ultimately ruled out for the remainder of the contest. Veteran Matt Moore replaced Mahomes under center.
The injury occurred during a quarterback sneak in the second quarter. Broadcast footage appears to show a Kansas City trainer popping the reigning MVP's right knee back into place.
The 24-year-old told head coach Andy Reid that he's "going to be fine" as he limped off the field, according to FOX Sports' Erin Andrews.
Mahomes came into the game with an ankle injury suffered earlier in the season.