Chile coach Jorge Sampaoli revealed on Tuesday that key midfielder Arturo Vidal is not guaranteed to face Spain in the World Cup Group B showdown between the teams on Wednesday.

The Juventus midfielder underwent knee surgery a month ago and played for only the first 60 minutes of Chile's 3-1 win over Australia in their opening game on Friday.

"I always said it was very difficult for him to join us here because he had a very serious injury and he had surgery," Sampaoli told a pre-match press conference at the Maracana in Rio de Janeiro on Tuesday.

"However, he managed to play some minutes against Australia and we'll see how he feels now. He's been training at a higher pace this week and we'll see if he can play some minutes tomorrow (Wednesday).

"We analyse his situation every single day. We know he's recovering now, he feels much better and he's here because he's really dedicated and willing to play.

"Arturo wants to play for the national team and we're very happy to have him here, if that doesn't damage him."

Victory for Chile could send Sampaoli's side into the last 16 and consign champions Spain to elimination, depending on the result of the day's other group game between Australia and the Netherlands.