England manager Roy Hodgson said he was unaware his side's supporters were chanting anti-IRA songs at Tuesday's friendly against Scotland.
Police in Scotland arrested 26 people for minor disorder offences including breach of the peace and drunkenness - seven in Celtic Park itself.
During the game, tensions ran high as each side booed the respective singing of their national anthems, and England supporters were heard singing ''F*** the IRA''.
"I was aware the crowd were tremendously supportive. I didn't have a clue what they were chanting," said Hodgson.
"I don't condone it. If anyone was offended, I'm sure the FA would like to apologise to them."