McCarthy was stretchered off and immediately taken to hospital for further assessment, and he is now expected to undergo more scans on Monday.
Muamba says the incident affected his game afterwards on Saturday, stating he was too worried about whether the youngster would be out of action for any length of time.
"I thought I had a 50 per cent chance of getting the ball as it was so direct to him," explained Muamba.
"I thought I could just nick it and push the team forward.
"When I came in so fast, I slightly nicked the ball and he landed awkwardly.
"I didn't go in to injure James, it wasn't planned or anything like that.
"I didn't want him to get injured or anything like that, so I regret it but I did just go in to get the ball.
"It messed me up when he left the pitch. I didn't really know what had happened to him so I was worried."