Following a solid display against Italy on Friday in which Ruiz scored the winning goal, Sunderland are thought to be pondering a move for the 28-year-old.
The Costa Rican netted five times in thirteen appearances during his loan spell in Eredivisie and PSV are likely to fight to sign Ruiz on a permanent basis, although recent comments made by the forward suggest his preference is to return to England and prove his worth in the Premier League.
Ruiz told the press: “I want to show the English what I am and that what happened at Fulham is not real.”
Gus Poyet will be keen to strengthen his striking options at the Stadium of Light in time for the upcoming season, with the immediate futures of Jozy Altidore and Steven Fletcher still uncertain.
Sunderland relied on a late run of goals from youngster Connor Wickham last term to escape relegation by the skin of their teeth and Poyet will not fancy trusting such a burden on the England under-21 international again.
If the interest in Ruiz is genuine, then it is likely to spell the end in Sunderland's pursuit of Fabio Borini.
Borini had been the Black Cats' number one target this summer following a fruitful loan spell at the Stadium of Light last season, but now following reports that the Italian has been offered to Southampton in a possible exchange deal for Adam Lallana, a move to Sunderland is looking less likely by the day.
Sunderland could face competition from Arsenal who are also rumoured to be interested in signing Ruiz.