Barcelona’s Dutch midfielder Frenkie de Jong is undergoing treatment on a torn knee ligament suffered while on national duty at the World Cup, the Spanish champions said on Thursday.

De Jong said the injury came to light on his return from the World Cup when Barcelona doctors returned a more serious diagnosis than the original assessment from the Dutch medical staff.

De Jong suffered “a tear of the medial collateral ligament (MCL) in his right knee,” Barcelona said in a statement.

“It has been agreed that the player will continue with conservative treatment under the supervision of the club’s medical staff. His progress will be monitored over the coming weeks.”

De Jong said he played through the pain at the World Cup where the Netherlands exited in the last-32.

“During the World Cup I injured my knee. After the first assessments, the (Dutch team) doctors told me it was a small injury and that it would not get worse if I continued playing,” De Jong said on Instagram.

“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.”

After starting in two group phase matches De Jong, 29, missed the Netherlands’ third game, a 3-1 win over Tunisia, but played 109 minutes of the penalty shoot-out defeat to Morocco in the first knock-out round.

The situation changed when he returned to club duties, where more intensive medical tests revealed the true extent of the damage.

“These 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,” he added.

Barcelona begin the defence of their Liga title away at Elche on 23 August.