Real Madrid head coach Zinedine Zidane is unsure how long Eden Hazard will be sidelined, but said the attacker was "upset" after another injury setback.
Hazard, 29, is enduring a torrid run in Madrid, and is yet to make an appearance this season, with doubts now over whether he'll fit for El Clasico later this month.
The Belgium international was ready to return from an ankle problem, but suffered a muscle injury that saw him miss Wednesday's 1-0 La Liga victory over Real Valladolid.
- Falcao making up for lost time at Rayo Vallecano as World Cup quest continues
- Gilberto Silva exclusive: Arsenal legend on Arteta, Edu, Partey's importance and beating Spurs
- Stop Lukaku, stop Chelsea? Tuchel needs big-money Blues attackers to help £98m star striker
- Man Utd misery: Fernandes penalty failure and defensive injuries pile early-season pressure on Solskjaer
Zidane is unsure how long Hazard, signed from Chelsea last year, will be unavailable.
"I can't tell you how long it'll be. He picked up a bit of a knock in training before the game," he told a news conference.
"It looked like a muscle spasm but in the end it turned out to be a bit more than that. It's something muscular. It's nothing to do with the injury he's had and these things happen.
"He's been out for a long time. I don't think this one will be long but I can't tell you exactly."
Hazard has struggled to impress since arriving at Madrid, where he scored one goal and provided three assists in 16 La Liga appearances last season.
Zidane said the former Lille star was disappointed after his latest injury but stressed the importance of keeping it in perspective.
"He's upset because he was all right. We talked about it at the press conference before the match, but he's had a setback and these things can happen," he said.
"He's not happy, he knows that it's not a big thing and we have to take it easy with him. It's a question of little time, I'm sure."
After earning seven points from their opening three La Liga games, Madrid visit Levante on Sunday.
Hazard's team-mate Thibaut Courtois sympathised with the Belgian star post-match and is hopeful he can bounce back quickly.
"Hazard is a little sad, he was training very well, it's a little setback. It's not the ankle," Courtois said. "I hope he's back soon. Hazard was looking forward to playing again."