The midfielder was delighted to be allowed to take part in the fixture where he will play alongside fellow United legends Paul Scholes and Ryan Giggs.
Beckham said: 'I think Bruce (Arena, LA Galaxy coach) knows how important it is for Gary. It’s more important than anything for me to be there for Gary.'
Arena has allowed Beckham, 36, to miss out on one of the club’s upcoming fixtures in order to make the appearance after admitting he was already set for a break. 'We’d be resting David in one of the games next week anyway.'
Along with Neville, former England captain Beckham formed the right hand side of a Manchester United side that won the treble in 1999. The news will be a boost for Neville, who also enjoyed a successful partnership with Beckham for England. Earlier in the week Neville said: 'I am in contact with David. It is looking positive but we still have a couple of things to sort out.'
The date of the testimonial - just four days before United's Champions League final clash with Barcelona at Wembley - has been criticised in some quarters but Neville is adamant that the timing is right. 'Hopefully it will be an enjoyable game for the fans and, four days before Wembley, it will be like a celebration and send-off for the lads who have done so well this season.'
Although Neville is due to begin work as a Sky Sports pundit, the 36-year-old clearly has no intention of stepping back from his barely concealed love of all things United. 'I am a fan. I have always been a fan,' he said. 'I wanted to do something for the fans and have said that publicly for the last 15 years.
'This is something I know will give me satisfaction and fulfil what I believe to be a thank you, so the fans can go and enjoy it.'
For tickets to Gary Neville's testimonial, visit manutd.com/tickets or call 0161 868 8000.
BECKS AND GNEV BACK TOGETHER!!!! I hope Becks brings his wooden spoon ...
ETA: So now that´s David Beckham, Phillip Neville, Paul Scholes, Darren Fletcher, Nicky Butt, Ryan Giggs & of course Gary who are confirmed to play in the game