CHELSEA may have to make an emergency move for a defender this summer after a shock injury to Levi Colwill.The Blues defender, who emerged as a key figure for Enzo Maresca last season, picked up a mystery problem in the Blues first training session of pre-season.GettyEnzo Maresca has said Chelsea may have to sign a new defender after Levi Colwill picked up an unexpected injury[/caption]AlamyColwill was injured during Chelsea’s first training session back for pre-season[/caption]Chelsea returned to training on Monday after their Club World Cup triumph last month, but were immediately brought back down to earth.Colwill was sent for a scan on Tuesday night with figures at the club concerned it could be a significant knock.Maresca hinted that, depending on the results of the scan, Chelsea may have to sign a replacement this summer.The Italian said: “We had a problem the last two days with Levi Colwill, that we don’t know how long he is going to be out.“We will see, hopefully not too long, but for sure it’s a problem for us. We need to wait, we don’t know yet.“It was in the first session on Monday, just in the last minutes of the session. He felt something and, as I said, we need to wait and then we see.”Asked whether they will now sign a replacement, Maresca added: “It depends. We need to wait and then we see.“But, as I said, we know each other from last year and, you know in our way, how important Levi has been.TRANSFER NEWS LIVE – KEEP UP WITH ALL THE LATEST FROM A BUSY SUMMER WINDOWBEST FREE BETS AND BETTING SIGN UP OFFERS“I spoke with him yesterday and I told him that if we achieve what we achieved last year, it is also because of him – and he was a main player for us.”Academy graduate Colwill emerged as a leader in Maresca’s squad last term, making 43 appearances in all competitions. While they may now need to add another defender, outgoings remain a significant part of Chelsea’s summer.Maresca has all but confirmed the open secret that striker Nicolas Jackson will be allowed to leave should the right offer come in.Chelsea value the Senegal international at £80million, with interest from Newcastle.The Blues boss said: “Nico is okay. He’s okay.“When the transfer window is open, unfortunately or fortunately, anything can happen. This also involves Nico’s situation.“At the moment we also had two strikers arrive, both of them in the USA, Joao Pedro and Liam Delap. So we will see what happens.”GettyNicolas Jackson is available for an exit from Chelsea this summer[/caption]