Atletico Madrid have confirmed that defender Juanfran suffered a Grade II muscle injury to his left thigh during their Champions League clash with Leicester City.
The full-back was forced off early in the second half of the 1-1 draw at the King Power Stadium and scans have since revealed the extent of the problem.
According to a statement on the Atletico website, Juanfran could face a spell on the sidelines.
"Our player will undergo physiotherapy and rehabilitation treatment," the statement read.
Atletico, who edged past Leicester into the semi-finals 2-1 on aggregate, face a mounting defensive crisis following the loss of fellow full-back Sime Vrsaljko to a knee problem.