Dimitar Berbatov is a doubt for Manchester United's mouth-watering Premier League clash with Aston Villa on Saturday after picking up a hamstring injury while on international duty.

The former Tottenham striker had to be substituted in the first half of Bulgaria's 6-1 defeat to Serbia in an international friendly in Belgrade on Wednesday.

Berbatov has scored six goals in 13 appearances for United following his £30.75million transfer from White Hart Lane at the end of August.

He failed to score in his first five games for Sir Alex Ferguson's side but broke his duck with two goals in the 3-0 Champions League victory at Aalborg in September.

After Bulgaria's limp display against Serbia, doubts have surfaced as to whether the 27-year-old is considering quitting international football.

His agent, Emile Danchev, was quoted in the Sun as saying: "Dimitar said to me that because people blame him for Bulgaria's bad performances, he is ready to quit the national team."