Alex Ferguson confirmed today that he has given permission to talk to Marseille about a loan move. Barthez, 32, is behind Tim Howard and Roy Carroll at Old Trafford and Ferguson has given him the go ahead to seek first team football elsewhere.
"He's going to speak to Marseille," said Ferguson. "They approached us a couple of days ago and there are one or two things to be ironed out.
"The reason I'm happy to let the move go through is that leaves me with two experienced keepers (Howard and Carroll)."
Barthez needs first team football if he is going to keep his place in the French national side, a point recognised by Ferguson.
"In fairness to Fabien the longer he's going to be here without getting a game there is going to be a problem for him.
"He's a terrific goalkeeper, one of the best in the world, but just by opportunity Tim Howard has taken the No1 jersey.
"Roy Carroll has done nothing wrong either so I'm being fair to everyone."
Marseille need a keeper to cover for injured reserve Cedric Carasso and, if the deal goes through, Barthez would challenge 27-year-old Croat Runje for the first-team shirt. The move for Barthez would have to be ratified by world governing body FIFA as it is outside the transfer window.
Barthez joined United for £7.8million in the summer of 2000 as Ferguson sought to fill the void left by the departure of legendary Danish keeper Peter Schmeichel.
After helping France add the Euro 2000 title to their 1998 World Cup victory, he signed a six-year contract at Old Trafford.
But his eccentric style eventually saw Ferguson eventually run out of patience and he was dropped towards the end of last season.