Bayer Leverkusen have confirmed they have received several enquiries for reported Manchester United target Hakan Calhanoglu.
Calhanoglu, 21, has established himself as one of the best young talents in the Bundesliga in recent seasons, and the free-kick specialist has scored 18 goals in 63 games in all competitions for Leverkusen.
Leverkusen CEO Michael Schade said they face a battle to hold onto the midfielder, who joined for €14.5 million from Hamburg last year.
"We want to keep Hakan, but there is an absolute limit," Schade told Sport Bild, which suggested his club value him at around €40m.
Sport Bild reported that Barcelona and Atletico Madrid had made enquiries in the summer while United have scouted Calhanoglu on a regular basis, including during last week's 4-4 draw with Roma.
"I am relaxed about that," Schade added.
Leverkusen were able to raise significant funds -- reported to be around €30m -- through the sale of South Korea international Son Heung-Min to Tottenham in the summer, which appears to have assisted in their efforts to retain Calhanoglu so far.
Leverkusen sporting director Rudi Voller told Sport Bild: "It is true that we had several enquiries, but we did not want to sell the player, which would weaken us."
The player's agent, Bektas Demirtas, suggested the Turkey international was happy to remain at the BayArena for now.
"It's about the best possible development for Hakan," Demirtas said. "Currently, things are going really well for him at Leverkusen."
Calhanoglu has yet to show his best form in the Bundesliga this season but has showcased his qualities in the Champions League, where he has scored twice and set up a further four goals.