LONDON: Premier League champions Chelsea will find it difficult to replace influential striker Diego Costa if he departs in the current transfer window, club legend Frank Lampard has said.

Costa, 28, has been Chelsea's top scorer in all three seasons since joining the club in 2014, leading them to two league title wins.

Earlier this month, the Spain international said that he would leave Stamford Bridge after being told by manager Antonio Conte that he was not a part of the club's future plans.

"He's a fantastic striker and we all saw that last season and since he's been at Chelsea. He would be very difficult to replace, there's no doubt about it," Lampard told Sky Sports.

"He's an all-round physical presence that also has the quality to get goals, that's not easy to find in the modern day."

Costa scored 22 goals in 42 appearances for the London side last season but the club have been linked with a move to get Everton striker Romelu Lukaku, who scored 26 goals last campaign, back to Stamford Bridge.

"He's (Lukaku) certainly developed to a huge degree since he left the club (in 2014), Romelu would certainly be a good option. The only thing Chelsea have to look at is the inflated market that is around now, it makes it very tough," Lampard said.

Costa has said he would favour a return to former club Atletico Madrid but the Spanish side are unable to register new players until January 2018 due to a transfer ban by the Court of Arbitration for Sport (CAS).