​Arsenal defender William Saliba suffered a serious back injury while representing France at the World Cup. The centre-back is expected to be sidelined for four to five months, per L’Equipe.The 25-year-old was forced off during France’s 2-0 semi-final defeat to Spain after struggling with persistent discomfort in his back.AdvertisementAdvertisementAdvertisementSaliba reportedly told international team-mate Dayot Upamecano moments before being replaced in the 30th minute, “I can’t take it anymore, my back is dead.”The injury has raised concerns over Saliba’s ongoing fitness issues. The Arsenal star had previously battled chronic back pain.His absence will come as a huge blow to Mikel Arteta, given the Frenchman’s importance to the Gunners’ defensive structure.The way Les Bleus’ defence capitulated when Maxence Lacroix came on to replace Saliba shows he operates on a different level.Saliba has established himself as one of the Premier League’s finest defenders, becoming a key figure in Arsenal’s domestic and Champions League campaigns.AdvertisementAdvertisementAdvertisementThe north London club must now find a solution, with Saliba’s recovery set to keep him away from action until well into the new season.However, Arsenal could already have the ideal replacement within their squad.Cristhian Mosquera should be allowed to step up and prove he can fill the void left by Saliba.The young Spanish defender showed plenty of promise last season, displaying composure on the ball, defensive intelligence and the physical attributes required to thrive at the highest level.While replacing a player of Saliba’s quality is no simple task, Mosquera has the tools to make the position his own.AdvertisementAdvertisementAdvertisementRegular minutes alongside Gabriel Magalhaes could accelerate his development and allow him to grow into a long-term solution at the heart of Arsenal’s defence.The opportunity may have arrived sooner than expected, but Mosquera has the chance to announce himself as a genuine first-team star.