Sky Sports sources understand Dimitar Berbatov is travelling for talks over a return to Bayer Leverkusen, while there is also interest from Bayern Munich and Anzhi Makhachkala.
The Manchester United striker has fallen down the rankings in Sir Alex Ferguson's plans and, with his current contract set to expire in the summer, he has been linked with a move.
Berbatov said in December he had no plans to leave Old Trafford, but he was on Sunday spotted taking a flight to Frankfurt, where he was expected to hold discussions with Leverkusen.
There has been talk of United offering the 30-year-old a 12-month contract extension, but there is also interest from Bundesliga giants Bayern Munich and wealthy Russian club Anzhi.
Berbatov left Leverkusen in 2006 to join Tottenham, before moving on to Untied in 2008 in a £30.75million switch, and his former club have already expressed an interest in resigning their former star man.
The Bulgarian has dropped to fourth choice forward behind Wayne Rooney, Danny Welbeck and Javier Hernandez this season at United and that could dictate a decision on his future.
Bayern are understood to have identified Berbatov as a replacement for Ivica Olic, with the Croatian forward expected to leave the Allianz Arena in the summer at the latest.