Luis Suarez was the centre of controversy against Valencia when it appeared he deliberately stamped on Aymen Abdennour.
Suarez opened the scoring for Barcelona just before the hour-mark in the 1-1 draw, but five minutes before the goal, television replays showed the Uruguayan appearing to stamp on the foot of Abdennour.
The referee did not spot the incident, and the former Liverpool striker put the visitors ahead from a tight angle after Messi's fine ball over the top of the Valencia defence.
Suarez later insisted there had been no intent, telling reporters: "I did not stand on Abdennour's foot on purpose. I turned around, I stepped on him and that is why I apologised."
Watch the video of the incident above...