The 22-year-old was attacked on Sunday evening and was forced to spend the night in hospital after blacking out following the assault
Pezzoni was out celebrating Carnival in a German disco when a man approached him. The assailant called out: "Hey, you w*nker," before punching the 22-year-old.
"I immediately called the police," Pezzoni confirmed to Express. "I blacked out and I went straight to the emergency room."
The former Germany Under-21 international spent Sunday night in hospital and will now visit a specialist.
Koln are enduring a difficult season in the Bundesliga, as Saturday's defeat to Nurnberg left Stale Solbakken's side in 14th place.