Chelsea midfielder Marco van Ginkel will miss the rest of the season after suffering a cruciate knee ligament injury during the League Cup win over Swindon Town.
The Dutch international was replaced by Ramires after just 10 minutes of the win at the County Ground on Tuesday and assistant boss Steve Holland said the 20 year old would undergo a scan to reveal the full extent of the damage.
While Chelsea are still to confirm the damage suffered by Van Ginkel, the player's agent Rob Jansen says his client will miss over six months of action, leaving him in serious doubt for the World Cup next summer.
"This is a terrible setback for the boy," Jansen told the Algemeen Dagblad.
"More than six months seems forever. The question is whether he is still in the picture for the Dutch national team. The boy now feels mostly sadness.
"He has to go through it and focus on Chelsea at the moment."
Ramires, who came on for Van Ginkel and scored Chelsea's second to set up a fourth round clash with Arsenal, was substituted at half time with a hip problem and is a doubt for the trip to Tottenham Hotspur this weekend.
Despite only making two international appearances for the Netherlands national team under Louis van Gaal, Van Ginkel was expected to compete for a place at next year's World Cup along with PSV Eindhoven duo Stijn Schaars and Adam Maher.
But the injury blow has all but ruined his hopes of featuring in Brazil next summer, not least due to his inability to secure regular first team football with Chelsea.
Van Ginkel had made two appearances this season prior to his full debut against Swindon, coming off the bench to play in the Premier League wins over Hull City and Aston Villa and is perceived to be a long-term replacement for John Obi Mikel, who has failed to settle during seven years at Stamford Bridge.
Manager Jose Mourinho is unlikely to delve into the transfer market in order to replace Van Ginkel - who was only expected to play a peripheral role this season- despite Chelsea being expected to fight on four fronts this season, with as many as 11 alternative midfield options available to him.