Real Madrid are concerned about the injury sustained by Trent Alexander-Arnold in Wednesday's LaLiga win at Athletic Club, sources have told ESPN, with the England defender set to undergo tests to determine the extent of the problem.
Alexander-Arnold was delivering one of his best performances in a Madrid shirt to date -- his cross-field pass setting up Kylian Mbappé's opening goal -- when he was withdrawn in the 55th minute of the 3-0 victory at San Mamés, and replaced by substitute Raúl Asencio.
The right-back appeared to suffer a muscular problem after kicking the ball upfield, limping on the sidelines before asking to be withdrawn.
Midfielder Eduardo Camavinga was also substituted with an ankle problem, although the issue is thought to be less serious, sources said.
Alexander-Arnold's debut season at the Bernabéu -- after joining from Liverpool in a high-profile move last summer -- has already been heavily disrupted by injuries.
Having earned his place in the Madrid starting XI in the Club World Cup, he picked up a thigh problem in September, and was absent for a month.
His absence came with Dani Carvajal also unavailable, meaning midfielder Federico Valverde had to fill in at right-back.
Since returning to fitness last month, Alexander-Arnold had faced some criticism for his displays -- coinciding with the team's struggles -- but he looked much improved against Athletic.