Van der Sar made a howler in the 2-2 draw with the Baggies in last weekend’s Premier League game at Old Trafford.
“The mistake was uncanny,” said the United boss.
“Here is a player with 130 caps for Holland and the most fantastic career you could imagine and he makes a mistake like that.
“You cannot even criticise him because he doesn’t deserve that.
“He is allowed to make one horrendous mistake in his life. It was at a time when we didn’t need it, of course, but it happens.
“You just have to wash it away.”