Diego Costa has started to say his farewells to his Chelsea team-mates with the Premier League champions facing the threat of suffering a striker crisis ahead of the new season.

Manchester United’s move for Chelsea’s top striker target Romelu Lukaku has left the London club in a difficult position, as they work to find out whether there is room to launch an 11th hour bid of their own.

Chelsea are yet to rule themselves out of the Lukaku race and have noted Everton’s denial that a deal with United is agreed. The Belgian had favoured a return to Stamford Bridge, which may yet be something Chelsea try to exploit.

Should they be forced to admit defeat, then Chelsea will have to switch targets and could renew their interest in Alvaro Morata, who they bid for last summer, or Alexis Sanchez, who Arsenal have insisted will not be sold to a Premier League rival. Torino’s Andrea Belotti is another option.

Chelsea head coach Antonio Conte is due to return to work on Sunday and was understood to be anxious about the club’s striker situation, even before United made their £75million bid for Lukaku.