Gareth Bale has suffered an injury setback and is now sidelined with a thigh-muscle strain, Real Madrid announced on Friday afternoon.
The club did not specify a timeline for his return, but Marca reported Bale could be out of action until December.
The Wales international has not played for Real since suffering a calf problem in a 3-1 Champions League win at Borussia Dortmund on Sept. 26.
He had returned to training last week and was named in Wales' squad for friendlies against France and Panama. However, the Spanish club decided that Bale would not join his national team this week and instead remain in Madrid with a view to making a possible comeback at Atletico Madrid in the derby on Nov. 18.
And he now faces another spell on the sidelines after picking up a fresh injury on Thursday.
A Madrid statement said: "Our player Gareth Bale, who felt some discomfort in his left leg at the end of Thursday's training session, today underwent various tests carried out by the Real Madrid Sanitas medical team.
"He has been diagnosed with a strain to the middle third of the adductor longus muscle in his left leg. His recovery will continue to be assessed."
Bale's latest injury is a further blow for Real coach Zinedine Zidane, with attacking pair Cristiano Ronaldo and Karim Benzema having struggled in front of goal in La Liga with each finding the target just once so far.
Bale has scored two goals in five league appearances for Real, who head into the game at Atletico in third position in La Liga, eight points behind league leaders Barcelona after 11 rounds played.
The 28-year-old forward also missed Wales' final two World Cup qualifiers last month as they failed to qualify for next year's tournament in Russia.