Inverness Caledonian Thistle manager Richie Foran feels Celtic defender Erik Sviatchenko should have been sent off in the 2-2 draw between the sides.
With the score at 1-1, Inverness midfielder Ross Draper went down under defender Sviatchenko's challenge just outside Celtic's penalty area.
However, referee Don Robertson took no action against either player.
"The referees have got to be brave," Foran said. "It's quite blatant, it's there for everyone to see."
Celtic went 2-1 up shortly after the incident but Caley Thistle drew level again late on through Alex Fisher.
"It was an obvious free-kick and then it's an obvious sending off," Foran told BBC Scotland.
"Ross has pushed the ball in front of the lad, he's got his body in the way, the player's took him down. I'm very disappointed with the decision, very, very disappointed."
Celtic counterpart Brendan Rodgers said: "I haven't seen it. Some people have said they've seen it seven or eight times and they're not sure."
The visitors took the lead through Tom Rogic's volley but Billy King's impressive strike levelled before Scott Sinclair continued his record of scoring in each of Celtic's Scottish Premiership matches so far this season.
Celtic - who beat Rangers 5-1 last week and then lost 7-0 to Barcelona in the Champions League on Tuesday - dominated the second half but could not get a third goal and eventually dropped league points for the first time this season.
"We should win that game fairly comfortably," said Rodgers. "It was on the back of a tough week, coming to a tough place. If we can't take the three points then one will have to do.
"Some of our movement, the tempo and the speed in which we attacked was brilliant, and I think you've got to credit the goalkeeper.
"The important thing was we were creating the opportunities and on another day we could have had another four or five goals."
Inverness keeper Owain Fon Williams made several impressive saves and Celtic also hit the goal frame on three occasions.
Fisher came off the bench to head in Greg Tansey's cross and secure the point that took Inverness off the bottom of the table.
"I told the boys at half-time we will get one more chance, believe it, we will get one more chance and we did," added Foran.
"The desire is there, the hunger is there, and there's still more to come from us, still more quality. When we do peak we're really going to punish some team, I really believe that."