The 30-year-old Bulgarian spent five years in the Bundesliga, and retains affection for a club he helped reach the UEFA Champions League final at the expense of United back in 2002.
Red Devils boss Sir Alex Ferguson has used Berbatov sparingly so far this season, but the talismanic striker has netted four goals in his past two outings - back-to-back 5-0 victories over Fulham and Wigan.
However, his long-term future at Old Trafford remains uncertain, and Berbatov continues to be linked with a move away from Manchester United when the transfer window reopens in January.
"It's more than a rumour," Ivan Dobrinov, a member of the group which represents Berbatov, told Bild. "Leverkusen have it on their minds to get Berbatov.
"There is contact, but nothing concrete yet. It all depends on United's plans.
"We wait until 2nd January. Until then, United have the option but if that does not happen then Berbatov would be a free transfer in the summer.
"The player has never forgotten Leverkusen, the club is still very dear to him. Furthermore, he has a good relationship with the leadership at Bayer."
Meanwhile, Leverkusen CEO Wolfgang Holzhauser echoed Dobrinov's comments saying: "I would even say that the contact is friendly. But there is certainly nothing concrete at the moment.
"I also read that Manchester United would like to extend his contract."
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