The skilful duo left Craven Cottage to join London rivals Tottenham Hotspur in August.
"I don't think Fulham fans have seen the best of me yet," Ruiz told Fulham's official magazine. "Last season I found it hard at times, and there were a couple of injuries too that didn't help.
"Of course, it could have gone better, but I did a few things to show people what I have, and for sure, this season I'll do my best for the fans.
"Mousa and Clint have both left. They were two players that could do many things on the football pitch. But now we don't have them, and as a result, I do feel a bit more responsibility on my shoulders. I know that I can make a difference."
Ruiz, who is a Costa Rican international, scored twice in 27 Premier League games last season following his £10.6m arrival from FC Twente.