Ruiz, 38, retired from the professional game following the World Cup in Qatar last year and has since taken his first steps into coaching with a role at youth level.
The former attacking midfielder, who is perhaps best known for his four-year spell at Fulham, is now the U17 coach at another of his former clubs, Deportivo Alajuelense in Costa Rica.
Ruiz is also well known for his two years at FC Twente, where he played a key role in current United assistant Steve McClaren&aposs famous league title win back in 2010.
The Costa Rican was back in Twente over the weekend, along with Erik ten Hag, for Wout Brama&aposs farewell match, where he says he received an invitation to come to Carrington.
“I keep myself fit,” he told De Telegraaf after the match . “I go to the gym, I play tennis and padel. The first six months after I stopped, I took completely time off and only spent time with my family. Now I have started as a trainer for the U17 of Deportivo Alajuelense.