The former England manager re-established his reputation in Holland when he steered FC Twente to a league title in 2010.
Ruiz explained: “McClaren has been a big influence. When I was playing for Gent in Belgium and had the chance to go to Twente I wasn’t sure because they were not one of the best clubs in Holland.
“But once I spoke to him he convinced me to go there because he said he knew me and my qualities and I could do well and make my next step in a few years. So I went and he really changed me.
“In the first year with him I scored 24 goals and we were champions for the first time in the club’s history so his influence on my career is great.
“I have heard his reputation went down a bit here but as a person and a manager I think he is really good; one of the best trainers I have come across in my career. He can see many things, things not everyone can see and I think he is still a really good trainer.”