David de Dean returned to Spain earlier this month to attend the birth of his first child and had to complete a period of isolation upon his return to England.
De Gea returned to the Aon Training Complex on Monday in keeping with all protocols and will presumably travel to Italy on Wednesday, for the Europa League last-16 second leg in Milan.
"It is interesting to see what happens," explains Irwin on MUTV.
“There are two games within three days, so that is up to Ole now.
“Dean didn't have anything to do [against West Ham] and he's had a run of games when he hasn't conceded many goals, so he will be well pleased with that.
“But going forward it is great for Ole to have good competition there. It is just one area of the football field when you are in, you are in. It almost feels like that.
“I don't know what the situation is at the moment. Dean has done nothing wrong and David has been away back in Spain. We will have to see in the next few days."