Thibaut Courtois
Chelsea goalkeeper Thibaut Courtois faces up to two months on the sidelines after injuring his knee during training. Getty

Chelsea have suffered a major setback in their bid to gain ground on Premier League leaders Manchester City after Thibaut Courtois suffered a serious knee injury during training. The goalkeeper has been immediately ruled out of the Blues' clash against Everton on Saturday, 12 September.

According to the Daily Mail, the Belgian international is expected to be out for at least two months. Courtois had returned to training following two appearances for his county in their Euro 2016 qualifiers against Bosnia-Herzegovina and Cyprus before he pulled up with the injury.

This will come as a big blow to manager Jose Mourinho, who is already making up lost ground on the league leaders after winning just one game in their opening four in the Premier League. City are currently eight points ahead of Chelsea, and Asmir Begovic will be called in to deputise for the Belgian stopper.

Courtois has not had a great start to the season as well. He was sent off during Chelsea's opening game against Swansea City and has since conceded four goals, two against West Bromwich Albion in a winning cause, and then a brace during their loss against Crystal Palace prior to the international break. The Belgium international's absence will be a big loss for the Stamford Bridge outfit, who face a tricky set of fixtures in the Champions League and Premier League in the coming weeks.

Chelsea's fears regarding the goalkeeper having damaged his cruciate ligament have reportedly been dismissed, but the doctors could not get an exact prognosis due to the swelling around the injury, but the report claims that the stopper has been warned of a lengthy absence. Mourinho and Chelsea could be regretting their decision to let Petr Cech join Arsenal earlier in the summer, despite possessing a quality 'keeper in Begovic.