Fuller suffered an Achilles injury after appearing as a substitute with the FA Cup final only three weeks away.
Manager Tony Pulis said: "We are not sure how bad it is. He's going off to have a scan so we won't know that until Monday.
"It is disappointing because Ricardo is a game changer from the bench. He can come on and do special things.
"There is a danger you think of Wembley before it comes along and then players take their foot off the pedal.
"We must not do it. The Premier League is still our main priority. We still need points."
Source: PA
Source: PA