​Alarm bells are sounding behind the scenes at La Liga giants Barcelona early this week. This comes amid the understanding that Frenkie de Jong has picked up a serious knee injury.Midfielder De Jong is for his part fresh off playing his part for the Netherlands at this summer’s World Cup.AdvertisementAdvertisementAdvertisementAfter the Oranje were sent packing in the Round-of-16, however, the former Ajax man agreed to return to base in Barcelona briefly on Monday, for a round of medical checks.And it was during these tests that a serious concern was revealed.As per a report from Marca, after De Jong was forced to make use of pain-killing injections to take to the pitch at the World Cup:‘The Dutchman has suffered a significant knee injury.’It is added that the finding has sparked ‘great concern’ amongst the Blaugrana medical staff, who fear that the 29-year-old could be sidelined for a spell of around four months.Conor Laird – GSFN