Elliott captained Leicester City to the League Cup in 2000
Matt Elliott and Phil Gilchrist will take part in the testimonial game for Joey Beauchamp and David Langan at the Kassam Stadium on 8 July.
The pair will join ex-United stars Malcolm Shotton, Paul Powell, Mike Ford, David Rush and Trevor Hebberd.
Alan Judge, Matt Murphy and Paul Kee will also play in the fixture that pits an all Ireland XI versus a Rest of the World XI.
Elliott and Gilchrist helped United win promotion to Division One in 1995/96.
Elliott, 42, joined Oxford in 1993 and made 181 appearances during his four-year spell at the club before leaving for then Premier League side Leicester City in 1997.
The ex-Scotland international, who has 18 caps for his country, spent eight years with the Foxes and captained them in their League Cup victory in 2000.
Meanwhile, Gilchrist, 37, first signed for United from Hartlepool in 1995, scoring 11 goals in 206 appearances for the U's before joining Elliott at Leicester in 1999.
Gilchrist went on to play for West Bromwich Albion and Rotherham United, but returned to Oxford in 2006, playing 42 more games for the club before announcing his retirement during the 2007/08 season.