The Costa Rican international passed a fitness test to feature against Southampton at the weekend, though he was unable to prevent his side from losing 2-0 on the South Coast.
Although he has admitted that he is still being troubled by the complaint, the 28-year-old is hopeful that he will be fully fit soon.
"I still have some problems with my back and we're working on that. It's getting better. Hopefully in the next couple of weeks it will be 100%," he told the club's official website.
Ruiz joined Fulham from Dutch side FC Twente in the summer of 2011.