The Costa Rican frontman landed awkwardly during Fulham's draw with West Brom in Saturday's Premier League clash at Craven Cottage and he was sent for a scan on Monday.
The results revealed that Ruiz has suffered a ligament strain and although it is not clear how long he will be sidelined, the diagnosis is more positive.
A statement on the club's official website revealed: "Following an awkward landing as he contested an aerial ball, Bryan suffered an injury to his left ankle. He was assessed on Sunday and, despite swelling to his ankle, was able to walk with minimal symptoms.
"He underwent an MRI scan on Monday which confirmed that it is an isolated ligament strain, with no clear fracture. The early signs suggest that the injury is better than first feared, although a recovery time cannot be estimated until the swelling has reduced."
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