Ms Guercio took a swipe at the Red Devils following deadline day links to Everton as the window entered its final hours.
The Blues are understood to have discussed the possibility of bringing Romero to the club before moving for Roma’s Robin Olsen.
But speaking before the Blues confirmed the signing of Olsen on Monday night, Ms Guercio took to Instagram to hit at the Old Trafford club.
She wrote: “Sergio Romero worked hard for this club. Last trophy they won, they lifted it with him.
“He helped the team reach 4 finals/semi finals and then was left on the bench only to lose them all.
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“It is time for them to return the opportunity and let him go. RESPECT FOR ONCE!!!”
But now Ms Guercio has elaborated on her frustrations and says she is ‘very sad’ that United did not sell her husband in the summer transfer window.
She said: “It was a very stressful day for us. I have to say that I am sad, very sad on one and happy on the other hand.
“I am sad because Sergio deserved the opportunity to go to another club, he has shown what he can do and he worked every day.
“Right now he is training, just like he has been every day since he was in Argentina because he is a professional.
“He loves what he does and gives his all every day. I have known ever since I met about his passion and his work and his family obviously.
“It is a very sad day because he desired the chance to go to another club. He has worked hard every day for this, because he gives his all for United and I think that his chances of playing for United have gone down.
“This doesn’t sound right to me. It doesn’t appear honest or professional or serious that they have to let him go. I am very sad because of this.
“On the other hand I am happy because all of the fans of the club have shown all their amazing support.”