Bayer Leverkusen chief Rudi Voller has told Chelsea they must wait to sign Kai Havertz.

Voller has confirmed Chelsea's interest, but insist no negotiations will be considered while they're still alive in the Europa League. Bayer meet Inter Milan in the quarterfinals next week.

"We know Chelsea are very interested in him," said Voller.

"But we won't let any player change before the end of the Europa League.

"If Chelsea want to sign Kai, they have to pay the transfer fee that we have announced."

Bayer are said to be seeking €100m to sell Havertz this summer.