Diego Costa is set to miss the first leg of Atletico Madrid's Champions League tie against Barcelona after leaving training early on Monday.
Atletico coach Diego Simeone has conceded it will be "difficult" for Costa to play on Tuesday after the Brazil-born striker completed just 10 minutes of training before limping off the pitch.
Costa has scored 32 goals in all competitions for Atletico this season - including six in the club's past five matches - but Simeone does not expect the 25-year-old to take part at Camp Nou.
"The doctors will assess his fitness, but I can't see him playing," Simeone told reporters.
"Having seen him at training I think it is going to be difficult for him to make it, but we will wait as there's still a long while to go yet."
Costa's absence would be a huge blow for Atleti as Simeone feels the forward is as important to the Vicente Calderon side as Lionel Messi is to Barcelona.
"Without doubt. Cristiano (Ronaldo), Messi and Costa, all have their own style, but are all equally important.
"I think that Diego is growing day by day and Messi is demonstrating what good those two months off did him and will go into the World Cup in top form."
A final decision on Costa's availability is expected to be made in the final hours before kick-off.