Berbatov has yet to get off the mark in the 2010 World Cup qualifying campaign as Bulgaria have drawn their first three games.
And Markov said: "Berbatov is an exceptional talent and I don't challenge his class. But I expect more efforts and more will to help the team.
"We don't have to forget that he's not alone in the national team and he can't win matches by himself but I expect more from him."
Letchkov believes the high-profile players should be giving more after Berbatov ran only 2,000 metres during the recent goalless draw with Italy.
He said: "We will not achieve much with such performances,' he said. 'We have to be realistic, the year is not 1994 (when Bulgaria reached the World Cup semi-finals) after all."