But, the true extent of the injury was revealed when Fuller underwent surgery.
"Ricardo had the operation on Wednesday and it revealed that the cruciate ligament was three-quarters removed," Preston physio Andrew Balderston told the club's official website.
"This will require an operation to reconstruct the cruciate knee ligament and he will be out for the rest of the season."
With Richard Cresswell out for Saturday's visit of Wimbledon, North End are short in the striking department and manager Craig Brown wants to bring a striker in on-loan - if he can.
"I did enquire about the availablilty of Aston Villa's Peter Crouch, but he too is injured so they won't be able to loan him out."