Shakhtar Donetsk's Romanian coach Mircea Lucescu underwent surgery in Bucharest on Sunday after breaking several ribs in a car accident on Friday.
"Right now Lucescu is in surgery. Romanian doctors do their best to stop fluid accumulating in his pleural cavity," the Ukrainian champions said on their website.
Lucescu, 66, also suffered a concussion when his car, in which he was a passenger, hit a tram, then collided with another vehicle before crashing at the side of the road.
"Mircea is not just the Shakhtar coach, he's my friend," Shakhtar's billionaire boss Rinat Akhmetov was quoted as saying by the club's website after visiting Lucescu in Bucharest.
"We really need him but I hope our coaching staff could do the job and prepare the team well. After such incident we have no choice but to win both the league and the Ukrainian Cup."
Shakhtar are in second place, trailing arch-rivals Dynamo Kiev by a point with 10 games remaining. The season resumes in March following a three-month winter break.
Lucescu has coached Shakhtar since 2004, leading them to five domestic league titles, three Ukrainian Cups and the UEFA Cup in 2009.