The 22-year-old was involved in a heavy challenge 12 minutes into his side's Copa del Rey match against Osasuna, and left the game on a stretcher.
It now seems that Pep Guardiola could be without the Spaniard for some time, with Barcelona announcing that initial tests pointed to ligament damage.
"On first examination, it appears that Andreu Fontas has injured his cruciate ligaments in his right knee - more tests will be done," Barcelona stated via Twitter.
Fontas, who has made three appearances for his country Spain at the Under-21 level, was representing his club for the sixth time this season.
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