The Brazilian defender was benched for Madrid's 5-0 La Liga win over Rayo Vallecano at the weekend and the problem will also keep him out of Wednesday's first leg.
"Marcelo has been diagnosed with a first-degree tear in his left hamstring during a series of tests," a statement on the club's official website reads.
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It's unknown as of yet how long exactly the 25-year-old will be out of action, but Wednesday's encounter at the Santiago Bernabeu comes too soon.
Marcelo has been a key figure for Madrid so far this season, making 33 appearances in all competitions.
The Brazil international's absence means Fabio Coentrao is likely to get the nod against Dortmund at left-back.
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