Mahomes completed 21 of 30 passes for 255 yards and a score before he exited with 7:44 remaining in the third quarter of the 22-17 win on Sunday at Arrowhead Stadium in Kansas City, Mo.
Mahomes took off for a run during the sequence before Browns linebacker tackled the All-Pro quarterback. Mahomes' head hit the ground as he was taken down.
Chiefs players had to help Mahomes get to his feet after the collision. The team's medical staff then came onto the field before they escorted Mahomes to the locker room. Backup quarterback Chad Henne finished the game for the Chiefs.
"He was injured and had to come out," Reid told reporters. "He got hit in the back of the head. It knocked the wind out of him and everything else.
"He is doing great right now, which is a real positive. He passed all the [tests] that he needed to pass. We will see where it goes from here."
Reid also credited the Chiefs' "intestinal fortitude" for holding onto the lead and earning the victory after Mahomes' injury. Wilson tweeted well-wishes for Mahomes after the loss. Mahomes confirmed in a Twitter reply that he was "all good."
"Obviously, I was very sorry to see him get hurt," Browns coach Kevin Stefanski said. "I hope that he clears and is better very quickly.
"He is a great player, a great ambassador for this league. You do not want to see anybody get hurt in those moments. That is a really good football team. We knew that going into it. They are deep really across the board. They have great players, and I really respect coach Reid, his staff and what they have been able to build there."
The Chiefs host the Buffalo Bills in the AFC Championship game at 6:40 p.m. EST on Sunday at Arrowhead Stadium. Mahomes will need to clear the NFL's concussion protocol before he is eligible to play in the game.
The process starts with rest until Mahomes' symptoms return to a baseline status. Mahomes then can resume cardio workouts and train, while assessed by the Chiefs medical staff. He later can resume weight training and non-contact drills before he is cleared for full contact and passes an independent neurological exam.