Grella has definitely been ruled out of the Asian Cup qualifier against Oman in Melbourne on Wednesday, and could return to Ewood Park for treatment.
Rovers have a crucial game against arch rivals Burnley in the Premier League coming up, and Sam Allardyce will be hoping he can recover in time.
The Ewood Park outfit were humbled 6-2 by Arsenal last time out and Allardyce will want all hands on deck against the Clarets.
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