The German World Cup winner is leaving for Chicago Fire after penning a one-year deal with the MLS side.
"I am sad to leave so many friends at Manchester United," the 32-year-old said. "But I am grateful to the club for allowing me the chance to take up the challenge at Chicago Fire."
Schweinsteiger's exit continues Mourinho's systematic destruction of the squad that Van Gaal built over his ill-fated two-year tenure at Old Trafford.
The Dutchman made 12 permanent signings totalling an outlay of over £250million.
But following Schweinsteiger's departure only seven will remain with Angel Di Maria, Victor Valdes, Memphis Depay and Morgan Schneiderlin all now out the door.
With the likes of Luke Shaw, Matteo Darmian, Daley Blind and Sergio Romero largely out of favour under the Portuguese that figure could well dwindle further.
Mourinho revealed earlier this week there were several players in the United squad he would not have signed himself as well as three in particular he would not have sold had he been in charge at the time.
“I think I found a sad club," he said about what the club was like in the summer. "Manchester United sold players that I would never sell and bought players that I would never buy but probably when I leave a club people say that.
"I would never sell Di Maria, Chicharito [Hernandez], Danny Welbeck. Never. No chance."