Paris Saint-Germain coach Laurent Blanc said he was concerned after top scorer Zlatan Ibrahimovic came off injured in Wednesday's Champions League clash with Chelsea.
The Swede had to be substituted midway through the second half of PSG's 3-1 quarter-final first-leg victory at the Parc des Princes after appearing to hurt his right thigh while playing a pass to Christophe Jallet in midfield.
"It's a muscular problem. He will see the doctor tomorrow (Thursday)," confirmed Blanc, who immediately decided to replace the striker with Brazilian winger Lucas.
"He wanted to continue but I thought honestly that it wasn't reasonable. I hope he comes back as soon as possible because we need him."
Ibrahimovic, who has scored a club record-breaking 40 goals in all competitions this season, including 10 in the Champions League, faces a race against time to be fit for the second leg at Stamford Bridge next Tuesday.