Lukaku’s arrival could spell the end of either Costa or Michy Batshuayi.
“I do not know – that’s a decision for the club,” said Costa when asked about a deal for the Toffees striker.
“Of course Lukaku is a very big player who played an impressive season. I hope he can sign at Chelsea because it’s a unique club.
“He is a big player and has an impressive future for himself. The past matches have proven that he has quality and scoring ability.
“He is a boy who will take great steps. Hopefully he will continue to grow – he has all the qualities to stay here. (Mickey) Batshuayi may stay because he’s young and I could be leaving.”