The 20-year-old Calhanoglu took the unusual step on Wednesday of going public with his desire to quit strugglers Hamburg after two seasons for Champions League football next season with Leverkusen.

But Bayer's director of sport Voeller has said only his current club, who had to win a play-off to avoid relegation, can decide his future as the Turkey midfielder has signed a four-year extension to keep him in Hamburg until 2018.

"The player has the wish to transfer from his club and to come to us," Voeller told German daily Bild.

"It's not a secret that we'd like to have him - and Hamburg have known that for a long time.

"If we were in the same position as Hamburg, we would consider what to do.

"The main thing is: Hamburg will make the decision and we will accept it."

Hamburg's director of sport Oliver Kreuzer insisted on Monday that Calhanoglu will stay with them.

But the Turkey midfielder earned the wrath of Hamburg fans on Wednesday by telling magazine Sport Bild: "I definitely want to leave Hamburg, my outlook for the coming season I can see, crystal clear, being at Bayer Leverkusen.

"I simply want to go as far as Cristiano Ronaldo or Lionel Messi, I also want to be a superstar, whom everyone is talking about."

His comments came just 105 days after signing a four-year extension with Hamburg and he wrote on his Facebook page: "My goal is to play at Euro 2016 with Turkey and I want to collect international experience as quickly as possible, please have some understanding for my big ambitions."

Should Calhanoglu stay in Hamburg, Leverkusen's Voeller says he has "a plan B and C" ready.

"One should not forget that in (Brazilian left-back) Wendell and (Swiss striker) Josip Drmic we have already made two top signings," said Voeller.

"Especially with Drmic, it was important to get in there early, because we are convinced he will have a strong World Cup for Switzerland."