Karim Benzema set to face weeks on sidelines after injury at Celtic
The France striker hobbled off after half an hour of Tuesday's game at Parkhead with Real running out the impressive 3-0 winners.
Real manager Carlo Ancelotti (63) initially downplayed the seriousness of Benzema's injury after the game in Glasgow.
But after medical tests back in Madrid on Wednesday the club released a statement diagnosing "an injury to the semitendinosus tendon and a strain to the quadriceps muscle in his right thigh".
"His recovery will continue to be assessed," the statement added.
Spanish sports daily Marca predicted Benzema would be out of action for up to three weeks and suggest he is setting his sights on a return against Osasuna on October 2nd.
That means the favourite to win next month's Ballon d'Or will miss the La Liga clash with Real Mallorca, the Champions League home game against RB Leipzig, the capital derby with Atletico Madrid and teaming up with his French World Cup-winning teammates in the international window at the end of this month.
France are due to face Austria on September 22nd and Denmark three days later in the Nations League as part of their preparations for the 2022 World Cup kicking off in Qatar in November.