Sundowns will collide with Messi and company at 18h15 at FNB Stadium in the inaugural Mandela Centenary Cup.
The friendly was arranged in honour of 'Madiba', who was due to turn 100 this year.
"I don't think [swapping a jersey with] Messi is my priority," Mabunda tells KickOff.com.
"I just want to thank God for the opportunity to be able to play against the best footballers in the world.
"It's never easy to get such opportunities. I would like to thank the president [Patrice Motsepe] for making it happen.
"I would also like to thank the supporters for always being there. For me it is to make the supporters happy. As long as the yellow nation is happy, personal glory doesn't mean anything to me."
Downs previously lost 2-1 to Barca in South Africa in 2007.