McAllister fell heavily in an aerial challenge with Celtic defender Momo Sylla and was stretchered off in considerable pain.
The youngster was rushed to the hospital to have the injury looked at and Aberdeen boss Ebbe Skovdahl (pictured) was hoping it was not serious.
"I honestly didn't see it because there were people in my way at the time," said Skovdahl.
"But I don't really want to say too much at this moment only that he has gone to hospital for x-rays."
