Karl-Heinz Rummenigge hopes to agree a contract extension with Bayern Munich's Miroslav Klose but admits the situation is difficult to predict.
Germany international Klose will be out of contract in the summer but it has been reported that a new one-year deal has been offered.
But the striker, who turns 33 next month, is said to want a two-year agreement and has consequently been linked with Valencia and AC Milan.
Bayern chairman Rummenigge told Munchener Merkur newspaper: "Miroslav Klose is on a deal to expire this summer and I am virtually unable to predict if we are about to reach an agreement with him.
"It's definitely about the duration of a new deal. It would be very good to reach this agreement. I would enjoy this."
Meanwhile, Bundesliga 2 top-scorer Nils Petersen of Energie Cottbus is a target for Bayern and Rummenigge hopes to complete a deal later on this week.
He said: "I am very optimistic we will be able to announce the signature of Nils Petersen from Energie Cottbus this week."