"Everyone went straight to see him. It's hard for him, it's hard for us," Ake said after the Dutch won 4-0 in a Euro warm up in Rotterdam.

De Jong, 27, was a doubt for the tournament even before Ronald Koeman's squad met up earlier this month.

The Barcelona playmaker's last appearance was in a Spanish Liga defeat to Real Madrid in April.

The Oranje start their European Championship campaign against Poland on June 16 and then play favourites France and Austria in Group D.

"Frenkie is an important player for us and he is super in the squad,"  Manchester City defender Ake said.

Koeman may also be without a second midfielder Teun Koopmeiners, who suffered an injury in the warm-up before the Iceland victory.

"It's not a good sign," Koeman said. "We'll do tests and we'll see where he's at."

In the Iceland win, Xavi Simons, with his first international goal, Virgil van Dijk, Donyell Malen and Wout Weghorst scored, following up Thursday's 4-0 victory over Canada.