Beckham will captain a Great Britain and Ireland XI, managed by Ferguson, against a Rest of the World team coached by Carlo Ancelotti on November 14 at Old Trafford.
A number of Beckham's former Manchester United team-mates will take part in the match, which aims to raise funds for UNICEF, but Keane will not be one of them.
Beckham wanted Keane to play, but the former United captain had to turn the offer down because he is busy that week due to his commitments with the Republic of Ireland.
"We have asked Roy but obviously he is on international duty," Beckham said of Keane, who is assistant to Republic manager Martin O'Neill.
"That is part of the problem with some of the other players we wanted to play.
"We have to pick a weekend where we felt we would get a lot of support and 3pm on Saturday does not happen very often."
Had Keane been able to accept the offer, it would have been just the second time the former midfielder had played for Ferguson since their famous bust-up in 2005.
Keane had been an integral part of Ferguson's team for 12 years, but Ferguson became angry with his captain after he delivered a damning critique of his team-mates on the club's in-house TV station MUTV following a defeat to Middlesbrough.
The Scot was unhappy about Keane's brutally honest assessment of his team-mates and shortly afterwards he was sold to Celtic.
Keane played again under Ferguson during his testimonial between United and Celtic in 2006, but the pair have had something of a frosty relationship since.
Ferguson and Keane traded jibes about each other in their respective autobiographies.
:: The UNICEF game featuring Beckham, which pits a Great Britain & Ireland XI v a Rest of the World XI is on 14 November, 3pm, at Old Trafford
Tickets available from manutd.com
Source : PA
Source: PA