Bayer Leverkusen admits persuading Rene Adler to sign a new contract could be difficult if Manchester United make an offer for the goalkeeper.
Adler is among several keepers reportedly on United's radar to replace Edwin van der Sar when the veteran Dutchman retires at the end of the season.
United's goalkeeping coach Eric Steele was in attendance for Leverkusen's 2-0 win over Schalke at the weekend, with Adler's opposite number Manuel Neuer also linked with the Premier League leaders.
Leverkusen hope to agree a contract extension with Adler, but are aware any move from United could lead to the Germany international leaving the club.
"There have been talks between the club and Rene Adler already, however we are still far off an agreement at this point in time," Leverkusen executive Wolfgang Holzhauser told BILD.
"If a club the size of Manchester United comes up, I feel signing a new deal with Rene Adler would not become easier."
General manager Rudi Voller added: "It's a usual circumstance in football to have players being watched by other clubs.
"We have the desire to sign a new deal with Rene Adler, this is a fact."