The Costa Rica international has struggled to adjust to the pace of the Premier League since his arrival from FC Twente on transfer deadline day.
"Fulham is a good team," Ruiz said. "It's an emerging club, which plays good football and also has a trainer who wants to play good football. I have not had an easy time, but I am sure I will get more opportunities and I will always do my best.
"In the Netherlands, I had another second to think, a big difference."