De Jong has been named in the squad for the tournament, where the Dutch take on Austria, France and Poland in Group D, but it is a gamble by coach Ronald Koeman on his fitness.

On Sunday, de Jong continued his individual training at the Dutch camp but told reporters afterwards: "I'm not fit yet, so I can't say I'm doing well."

De Jong had three ankle injuries last season, in September, March and April, when he left the field on a stretcher playing for Barcelona against Real Madrid and has not competed since.

"The ankle is fine in itself but it just needs to recover properly because it shouldn't become something chronic," he said.

In training at the weekend, De Jong dribbled briefly with the ball but then dropped out.

"I'm not doing anything with the team yet. I am doing physio and recovery training, individual training. We just have to wait and see how the ankle goes. Then we will see when I can join in."

Asked whether he would be fit for the Dutch side’s first game against Poland in Hamburg on June 16, de Jong responded: "That is of course always the question. I mean: if you are not completely fit now and are not training with the group, then the question is always when and if you will make it. No one knows exactly.

"I really cannot say when. And that's not because I don't want to, even though I know it myself. It's just difficult to say."

Koeman last week said he expected his playmaker to be fit again for the first match against Poland.