Beckford, who spent the latter half of 2006/07 playing alongside Sparrow in the Iron team that won the League One title, will instead concentrate on preparing for the play-offs with his club Leeds United.
The May 4 game at Glanford Park will comprise two sides made up of former Scunthorpe players.
"I was asked to play, but we've qualified for the Play-Offs and that is obviously the priority," Beckford told Leeds' official website.
"The timing of the game means it's just not possible to play. Matt has been a good servant to Scunthorpe and I wish him well for his testimonial game. I hope everything goes well for him on the day."