"It was a difficult decision but sometimes we have to take difficult decisions," the Manchester United striker told a news conference at the Vasil Levski national stadium.

Berbatov, 29, represented Bulgaria 74 times since making his debut in 1999 to become his nation's all-time leading goalscorer with 48 goals.

The former Tottenham forward's future with United is reportedly in jeopardy following a less-than satisfactory season at Old Trafford.

Rumor has it that Sir Alex Ferguson is looking for a big-name striker to support marksman Wayne Rooney upfront.