Barcelona midfielder Frenkie de Jong will miss the start of the new season and could be set for months on the sidelines with a knee ligament injury.
De Jong, 29, started all four games at the World Cup this summer as the Netherlands crashed out in the round of 32 to Morocco, but returned to Barça with the injury this week.
"Medical tests have confirmed that De Jong has suffered a tear of the medial collateral ligament (MCL) in his right knee," the Spanish champions confirmed on Thursday.
"The player will continue to undergo treatment under the supervision of the club's medical staff, with his progress to be assessed over the coming weeks."
Barça have not specified how long De Jong will be sidelined, although surgery has been discarded as an option for now.
However, a source told ESPN there is no chance he will be ready for the team's LaLiga opener at Elche on Aug. 23, while in the worst case scenario he could miss several months of football.
Later Thursday, De Jong released a statement explaining how he had obtained the injury following claims he had prioritised his country over his club by playing through the pain barrier at the World Cup.
"It's difficult for me to see people questioning my relationship and commitment to the club because of false reports," De Jong said.
"Football is everything to me. I have always given everything I have for Barcelona and my country. That is why I want to share what happened.
"During the World Cup, I injured my knee. After the first assessments, the doctors told me it was a small injury and that it wouldn't get worse if I continued playing.
"The only challenge was playing with some pain, but throughout my career I have done that whenever I could contribute to the team, both for my club and my country.
"Further examinations [in Barcelona later] showed that the injury was more serious than initially determined. Thankfully, at this stage there is no need for surgery, and I am now fully focused on my recovery and returning to the pitch as soon as possible."
De Jong suffered several fitness issues last season, although most of them were muscle-related.
He missed 11 matches at the back end of the campaign with a hamstring injury, but returned to fitness to play for his country at the World Cup in North America.
After playing 90, 59 and 72 minutes in the group stage games against Japan, Sweden and Tunisia, De Jong played 110 minutes in the Netherlands' penalty shootout defeat to Morocco.
After the game away at Elche, Barça have back-to-back home games against Athletic Club and Rayo Vallecano as Hansi Flick's side begin their defence of LaLiga.
In theory, they are well stocked to cope without De Jong, with Pedri, Gavi, Marc Bernal and Marc Casadó all options to play at the base of the midfield, where Eric García, Andreas Christensen, Dani Olmo and Fermín López have also been used.
Barça's focus is currently on strengthening the attack, with Borussia Dortmund's Karim Adeyemi becoming the club's second signing of the summer on Thursday after the arrival of Anthony Gordon.
ESPN have previously revealed that young Belgian winger Jesse Bisiwu is set to follow Adeyemi and Gordon in the door at Camp Nou, with a No.9 also wanted to replace the outgoing Robert Lewandowski.
Julián Álvarez remains the No.1 target, while the club could also sign a centre-back and full-backs, with João Cancelo likely to return after a successful loan spell.