In a statement, league officials said Collins "violently and unnecessarily struck a defenseless receiver" in the neck and head area with his helmet during Sunday night's game at Lambeau Field and called it a "flagrant violation of player safety rules."
The NFL is cracking down on illegal hits, and players who violate the rules are subject to increased fines or even suspensions.
Williams said after the game that he didn't think NFL Commissioner Roger Goodell should punish Collins for the hit.
"Commissioner Goodell, don't fine the guy," Williams said. "It wasn't that bad of a deal, he shouldn't get fined. It was a football play, a football player making a football play. No injury, no harm."
"It was a bang-bang play and I felt that really when I saw the replay on the Jumbotron, it looked like Nick hit Roy in the back and came up to the helmet," McCarthy said Monday. "I understand why Rick threw the flag and we actually talked about the mechanics of it. That's a tough call.
"I think the referees are doing a very good job with the awareness of player safety, but I was standing right there and I can see what Nick Collins saw, too. The ball was in the air and he was trying to run through the proper target line and I think he hit Roy in the top of the pads and went up into the helmet."
The Associated Press contributed to this report.