Terms of Fua's deal were not released Wednesday.
Fua was Carolina's third-round draft pick in 2011 but was cut on Aug. 31 after getting beat out by rookies Star Lotulelei and Kawann Short.
Fua played in 24 games with 12 starts the last two seasons with Carolina.
Williams injured his knee in Carolina's 12-7 loss Sunday to Seattle. Chris Scott is expected to start in his place Sunday at Buffalo.
Carolina also made two practice squad moves, signing offensive lineman Mike Jasper and re-signing defensive tackle Casey Walker.
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