During his active days, the 43-year-old claimed six Premier League titles, two FA Cups and one Champions League silverware at United before heading to Real Madrid for £25m in 2003.
He said: 'I'll be back in Manchester on May 26 to play in this game against Bayern Munich'.
"To be back together as a squad and to be managed by the boss again is huge".
Manchester United came back from behind to beat Bayern at Camp Nou in 1999 thanks to two injury-time goals by Teddy Sheringham and Ole Solskjaer to lift the trophy for the second time in the club history, adding to the Premier League and FA Cup they had won earlier. "I can't wait", he stressed.
A historic Treble in 1999 formed part of his story at the Theatre of Dreams, and that success is about to be honoured in a reunion match.
United interim boss Ole Gunnar Solskjaer, who scored the injury-time victor in 1999, is expected to be in the side.
It has already been confirmed that Gary and Phil Neville will combine with Denis Irwin and Jaap Stam in defence, in front of goalkeeper Peter Schmeichel.
Proceeds from the game will raise funds for good causes supported by the Manchester United Foundation.