(CNN) -- Italy have admitted they do not know when star goalkeeper Gianluigi Buffon will be able to return to action at the 2010 World Cup.
Buffon, who helped Italy win the tournament in Germany four years ago, had to be substituted at half-time during his team's 1-1 draw with Paraguay on Monday because of a sciatic nerve problem.
The Juventus stopper initially said he hoped "to recover in two days" but an official Italy team statement was less optimistic.
"[He] has a strong sciatic problem," it read. "It's impossible to estimate when he might return."
Italy's next match is against New Zealand on Sunday June 20, with a contest against Slovakia four days later.
The Azzurri had to come back from a goal behind against Paraguay and will need to improve dramatically if they are to win the tournament and match Brazil's record haul of five World Cups.
Meanwhile, Dutch winger Arjen Robben is still eight days away from full fitness, according to Netherlands coach Bert van Marwijk.
Robben was back in training on Tuesday following the hamstring injury which ruled him out of their 2-0 victory over Denmark, but is likely to miss the June 19 clash with Japan.
Spain midfielder Andres Iniesta is fit for Spain's opening World Cup match against Switzerland on June 16 after overcoming a thigh injury.
And England duo Ashley Cole and Wayne Rooney returned to full training on Tuesday having rested on Monday to recover from the 1-1 draw with the United States.