Arturo Vidal has suffered a further injury setback, the Bayern Munich midfielder unable to complete training on Sunday.
Vidal has not played for Bayern since coming off in the Champions League quarter-final first-leg win at Sevilla with a knee injury on April 3.
And having felt pain in his right knee during Sunday's session, Vidal could be a doubt for the semi-final against Real Madrid, the first leg of which is 10 days away.
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"Vidal had to break off the session," Bayern said in a short medical update.
"The 30-year-old will undergo a thorough examination, an exact diagnosis will follow on Monday."