"I felt something hit me on the head, then I saw a knife on the ground and thought it had touched me," the Italian international said. "I didn't want to believe it - it seemed impossible."
The midfielder carried on playing after the second-half incident but had five stitches in the wound after the match.
A 16-year-old Parma fan also suffered a knife wound in a minor scuffle.
Fiorentina, the Italian league leaders, shook off the effects of their surprise 2-1 defeat away to Roma at the weekend to beat Grasshopper 2- 0 in Zurich.
The Argentinian Gabriel Batistuta scored from a pass by Edmundo in the 20th minute. Anselmo Robbiati took advantage of sloppy defending to power in a fine header just three minutes into the second half to leave Fiorentina well placed to go through to the third round after the second leg in a fortnight's time.
Sylvain Wiltford scored with an overhead kick a minute before half-time to give the French league leaders Bordeaux a 1-0 victory over Vitesse Arnhem in the Netherlands.Reuse content