​Barcelona are reportedly furious with the Netherlands and coach Ronald Koeman after discovering Frenkie de Jong has a potentially serious knee injury that is expected to keep him sidelined for some time.The injury was picked up when De Jong returned for medical checks at the start of the week. Barca are said to fear the worst and believe he could be set for several months on the sidelines.AdvertisementAdvertisementAdvertisementAccording to AS, the medical check-up found that the “knee was completely unstable and that there could even be ligament damage.” Further tests are due to be carried out because “the internal bleeding prevented an MRI scan from being performed.”Barcelona are pessimistic about the outcome and fear De Jong will need to go under the knife which could see him sidelined for around 4-6 months.AS also add there is “monumental anger” at the club as they feel “misled” by the Dutch team. Barca knew De Jong had injections to play against Tunisia and Morocco at World Cup 2026 but weren’t aware of the severity of the injury.Barcelona are also frustrated with De Jong and believe he should not have pushed himself to play through the injury which could now see him forced to undergo surgery.