Trent Alexander-Arnold faces two months on the sidelines after picking up a hamstring injury in Real Madrid's Champions League opener on Tuesday, sources told ESPN.
The 26-year-old was forced off just five minutes into the 2-1 comeback win against Marseille at the Bernabéu, where replacement Dani Carvajal was later sent off.
Sources told ESPN that Alexander-Arnold will be out for six to eight weeks and will miss the derby against Atlético Madrid and is unlikely to be ready in time for El Clásico against Barcelona.
The same sources suggested that the recovery time could be shortened due to the former Liverpool player's good physical condition, but are unwilling to take any risks.
Madrid said in a statement on Wednesday: "Following tests carried out today by the Real Madrid medical services on our player, Trent Alexander-Arnold, he has been diagnosed with a muscle injury to the biceps femoris in his left leg. Further updates will follow."
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Alexander-Arnold was overlooked by Thomas Tuchel for England's September fixtures and the hamstring injury not only looks set to rule him out of the next camp but could stop him returning to Anfield with Real.
The right-back ended his 20-year association with Liverpool in the summer but had been set to return with Alonso's side on November 4.
Information from PA contributed to this report.
