Netherlands centre-back Joris Mathijsen is "80 percent out" of their Euro 2012 Group B opener against Denmark on Saturday after suffering a setback in his recovery from a hamstring injury, coach Bert van Marwijk said.
Mathijsen again trained on his own for almost the entire session on Wednesday but he could only jog gingerly and did not touch the ball.
Van Marwijk told a news conference: "I am willing to take a risk but we will see in the next two days what will happen."
Wilfred Bouma, who only made the squad at the last minute, is being tipped as a potential replacement for Mathijsen given his greater experience than the other contenders.
Mathijsen was injured during the 2010 World Cup finalists' 2-1 loss to Bulgaria in a friendly last month.