LONDON: Chelsea manager Antonio Conte is uncertain about the future of Diego Costa, as Spanish media reports have linked the striker with a possible return to Atletico Madrid.

The 27-year-old, who joined the London club from Atletico in 2014, did not feature in Chelsea's 3-2 defeat by Real Madrid in a pre-season friendly on Saturday due to a back injury.

The Spain international scored 12 times last season as the club finished 10th in the Premier League, with British media reports also linking Everton striker Romelu Lukaku with a potential move back to Stamford Bridge.

"To play as a second forward he must improve his shape but he is working and he knows his shape in the same way as the other players."

Chelsea begin their league campaign with a London derby against West Ham United at Stamford Bridge on August 15.