"It's true, an official summon has been sent," Penev was quoted as saying on the Bulgarian Football Union's website. "We'll have one more talk (to clarify things)."
Berbatov, who completed his move from Manchester United to Fulham on the frantic final day of the transfer window, quit the Bulgarian national team in 2010.
His unexpected retirement from international soccer was met with a mixture of anger and, in some cases, a strong sense of betrayal in his homeland.
Earlier this year, however, Berbatov said he would be open to an approach from Penev after he moved to a club where he could play regularly.
The 31-year-old, who is Bulgaria's all-time leading scorer with 48 goals, will hold a news conference in Sofia on Monday to discus the issue and his protracted transfer saga.
Berbatov angered Serie A side Fiorentina when he turned his back on them after agreeing personal terms so that he could join Juventus. But in another twist, the player did the same to the Italian champions in favour of a move to Fulham.
Bulgaria host Italy on Sept. 7 before they face Armenia four days later.
- Bulgarian Football Union
- Manchester United