Zaha is reportedly furious with Crystal Palace after they failed to sell him before Thursday's transfer deadline.
It's not difficult to understand why Palace were hellbent on keeping their academy graduate.
The 2018/19 campaign was Zaha's best at Selhurst Park, notching 10 goals in 36 games and being a general terrifying presence for opposition fullbacks.
The main (if only) criticism of Zaha are accusations of simulation that have dogged his career.
The winger has protested his innocence and last year stated that there was an "agenda" against him after he was booked for diving.
Either way, Zaha will continue to get kicked every week as he dazzles and dances past defences.
And Class of 92' graduate Thornley thinks the 26-year-old can become an even better player if he perseveres through those inevitable tough tackles.
He told Tribalfootball.com: "I think Zaha is ready to step up another level. I've seen him on numerous occasions both in and out of a United shirt.
"He's got absolutely everything you would need to succeed at the highest level and I'm a massive fan of Zaha but he's one of these players that every time someone touches him his arms are up in the air to referee.
"If he's going to get kicked he should take it as a compliment, he needs to get on and say if you're gonna kick me that means that I'm to quick for ya and I tell ya what I'm going to pick up the ball and run at you again, until you get a yellow card, until you get a red card. That is the sort of player that any defender would not want to be facing week-in, week-out.
"I thought he would have been a really good fit for Tottenham, and then Arsenal fell well below Palace's valuation, but whoever he signs for are getting a great player."
Zaha's career at Manchester United ended far too prematurely, according to Thornley.
He returned to Palace on loan in the summer of 2014 and never returned, and Thornley says he was sad not to see Zaha given a chance to light up the Theatre of Dreams.
"I thought he certainly had the ability to succeed at United but Moyes never really gave him the chance to prove that on a regular basis.
"He then decided that he was too good to sit on the bench and returned to Palace and now he's on the verge of greatness by moving to a big club for a lot of money. He invariably is going to be the difference in matches because of the ability he's got to win games by himself. And I'm just sorry that he never got the chance at Old Trafford because he's an extremely exciting player to watch."
Zaha has missed out on leaving the South London club and has reportedly been promised the chance to depart in January.
But with the signing of fellow winger Daniel James this summer, Thornley believes you can rule out a return to United.
He continued: "I think that with the acquisition of James and we know that Zaha prefers to operate from the left Im pretty sure we wouldn't go for Zaha.
"We've been linked with a lot of players but Zaha's not one of them and I don't think we would be spurring him now that we have Daniel James, but I do feel he will end up going somewhere."