Strathclyde Police are to investigate the half time melee that saw Robert Douglas and Thiago Motta sent off in Celtic's Uefa Cup clash with Barcelona.
Rab Douglas insists that he was acting as peacemaker
"Following a number of reports made to police, further enquiries are now being conducted," read a statement.
Celtic boss Martin O'Neill will now examine BBC footage and may appeal the decision to avert a goalkeeping crisis.
Douglas' red card could leave Celtic with only one fit number one for the second leg in Spain.
O'Neill is likely to find pictures inconclusive and may recall Magnus Hedman from loan in Italy.
But Hedman has had an operation, January signing Danny Milosovic has also been injured, so 19-year-old David Marshall is standing by to play.
A Uefa spokesman said it would be unusual if German referee Wolfgang Stark's decision was overturned on appeal.
So O'Neill might be forced to turn to Sweden international Hedman, who was loaned out to Ancona after losing his battle with Douglas to be first choice.
Uefa have given Celtic the go ahead to draft him in, because Milosevic has been absent with a back problem and personal problems.
"I will certainly have a look at all situations and examine things in the next couple of days," said O'Neill.
"Danny Milosevic has signed for us and I have spoken to his agent about this morning and he wants to come back here.
"With Magnus, I will have to wait and see what the rules are. If that was a possibility, that would be the first option."
However, O'Neill says he would have full confidence that David Marshall, who replaced Douglas on Thursday, could handle the hostile atmosphere he would face in a packed Nou Camp.
"If something is sorted with Rab Douglas then that would alleviate the problem and if not then I am happy with David Marshall going into goal," said the Celtic boss.
Reports have suggested that Douglas had been attempting to calm down tempers after a heated exchange involving team-mate Neil Lennon at half-time of a tie eventually won 1-0 by Celtic.
"There were a number of people in the area," O'Neill told Celtic's website. "Perhaps someone had a particularly clear view.
"I do know that Rab feels exceptionally hard done-by because, whatever happened in there, he felt he was going to intervene.
"I'm not sure if it was fourth official who spotted something."
The red card rules Douglas out of the second leg of the fourth-round tie and only he, Hedman and Marshall are registered for European competition.
Should Milosovic and Hedman be ruled out through injury, the Glasgow club would have to apply for special permission to sign another goalkeeper.
A yellow card for Bobo Balde has also ruled the defender out of the second leg and increased the problems facing O'Neill.
Injuries meant that Celtic could only list six out of seven possible substitutes against Barcelona.
Barcelona midfielder Motta will also miss the second leg, along with striker Javier Saviola, who was sent off during the second half.