Ryan Christie has suffered either a broken eye socket or a broken cheekbone, according to manager Neil Lennon.
The Celtic midfielder saw his Scottish Cup semi-final appearance end before half-time after a sickening clash with Dominic Ball.
The Aberdeen defender was late with an aerial challenge and caught Christie in the face with his forehead.
A second yellow card was shown by referee Craig Thomson. The Dons were later reduced to nine-men after Lewis Ferguson was shown a straight red card for a two-footed lunge on Tom Rogic as Celtic ran out 3-0 winners.
Speaking to BBC Scotland, manager Neil Lennon said: “We saw him at half time and he was conscious. We think it’s either a broken eye socket or a broken cheekbone.
“It was a horrendous coming together and I don’t think there was any deliberation over it. It was a definite second yellow.”