The 55-year-old has been appointed as the sporting director of French club Strasbourg.
He left his previous position as technical director at Brighton in September, having also worked as the pathway development manager for the Premier League side.
Mr Weir said: "It is a great honour to join Racing, a historic club with a strong identity and growing ambition.
"I was convinced by the project and the quality of the people already in place.
"I am eager to settle in Strasbourg and become fully involved in the life of Racing.
"I look forward to working with Liam [Rosenior] and all the teams to contribute to Racing's success this season and in the years to come."
Strasbourg, the sister club of Chelsea, was bought over by BlueCo in 2023.
It's said that Weir will work closely with the London side.
The link between the clubs is already evident, with Mike Penders, Mamadou Sarr, and Kendry Paez currently on loan at Strasbourg from Chelsea.
During the summer, the Blues also sold Mathis Amougou and Ben Chilwell to the Ligue 1 club.
Weir was seen at Old Trafford with Chelsea co-owner Behdad Eghbali in recent months.
In a statement, Strasbourg said that Weir's appointment was "part of Racing's commitment to strengthening the structure of its sporting department."