Sunderland were battered 4-0 by Cardiff City yesterday, and Ruiter’s error was the turning point in the game.
Sunderland had held on in the first-half, and went into the break with the scores locked.
However, Ruiter tried to punch a corner kick and completely missed the ball, which allowed Cardiff to score their first.
The Bluebirds then went on to net three further goals, to pile the misery on Sunderland.
And Gray said: “It was catastrophic mistakes, firstly from Ruiter. It can’t happen. He’s running around players, flapping his arm at it.
“This is an experience goalkeeper. He’s making silly mistakes every week, that why he can’t pick between two goalkeepers.”
Chris Coleman could have the option of turning to Jason Steele, but the former Blackburn Rovers man has looked far from solid during his time in net this term.
Coleman initially helped to improve Sunderland, but the Black Cats have been in abject form again lately.
Sunderland are now winless in three games, and sit rock bottom of the Championship table.