A broken hand robbed Main of a chance to bid farewell to Saints fans at the end of this season, with the 42-year-old having now been released by the club but he is determined to play some part in the friendly against United at McDiarmid Park on July 31 (kick-off 2pm).
The club's record appearance holder told Saints' official website: "A broken hand is certainly not going to stop me from playing.
"The cast needs to come off and, when it does, I start rehab work immediately and I'll have a velcro strip on for added protection.
"It will be a special occasion all round. I'm glad it is a glamour game for the fans and it will give me a chance to say goodbye properly.
"Damaging my hand put me on a bigger downer even than when I broke my leg earlier in my career. I had been working hard for my chance to get a shot back in the first team before the end of the season and so the injury was badly timed."
Main thanked manager Derek McInnes for including the fixture in his pre-season plans.
He said: "The manager has been very accommodating and I owe him a massive thank you. Hopefully, the game will provide the ideal test for Saints as they work towards the new season."
The match will be United's second visit to McDiarmid Park.
They were the side who officially opened the stadium back in October 1989 when a Brian McClair goal gave them a 1-0 win.