"I'm shocked," Vasev, who is a Bulgarian under-19 international, told reporters on Wednesday. "We were walking and eight boys stood in our way.
"One of them hit me and I reacted to keep my dignity but at that time another lad stabbed me in the back," added Vasev, who was taken to hospital with non-life threatening injuries. His condition is said to be stable.
Vasev, widely considered as one of the most talented young players in Bulgaria, has played several matches for Slavia's first team.
Earlier this month, two Cherno More Varna fans were stabbed and three more seriously injured in clashes following the club's 3-1 win over Levski Sofia in the Bulgarian league.
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