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. 'Today Costa is Chelsea's player. Tomorrow if you ask me if Costa will remain with us, I don't know,' Conte told reporters. 'I can say that today Costa is a Chelsea player. He didn't play in these games because of injury and if he solves the injury and I see in training he's in good shape, it can be possible to see him in the next game against AC Milan.' Conte also added that playmaker Eden Hazard needed to work on his physical strength and fitness to play as a forward, after the Belgian came off the bench to score twice in the friendly against Real Madrid. 'Eden Hazard played 30 minutes and he is recovering a good shape,' the Italian added. 'I like him in this position, like a forward, and he can be a good solution for us... also playing as a winger. '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.