Joel Thomas is leaving behind Alvin Kamara for the possibility of coaching Saquon Barkley.

The Giants hired Thomas as their running backs coach — a lateral move for an assistant who spent the last nine seasons in that role for the Saints.

Thomas is the only known interviewee in a search that officially wrapped up within a week, though head coach Brian Daboll had a jumpstart on making his list of candidates because it was an open secret for about a month that Jeff Nixon was leaving after the season to be Syracuse’s offensive coordinator.

The reason for Thomas’ availability became clearer earlier Tuesday when the Saints fired Pete Carmichael Jr. — the NFL’s longest-tenured offensive coordinator, dating to 2009 — and two other assistants in an overhaul of an offense left over from the Sean Payton regime.

The Giants also re-hired Aaron Wellman as executive director of player performance.

He ran the strength and conditioning program during the Ben McAdoo and Pat Shurmur eras before spending the last four years at Indiana. The Hoosiers changed coaching staffs this offseason.

Wellman replaces his own successor, Craig Fitzgerald, who joined the Florida staff.

One of the main points of focus will be figuring out how the Giants can change a pattern as one of the most-injured teams in the league over the last decade.

Thomas is the Giants’ fourth running backs coach in as many seasons and could be Barkley’s fifth in seven seasons.

Barkley, who led the Giants in yards and touchdowns from scrimmage yet again, is a free agent who is resistant to a second franchise tag.

It is unclear when or if the Giants will tag Barkley anyway, offer him a multi-year extension or let him test the open market.

The depth chart behind him needs replenishing, with little-used rookie Eric Gray and special-teamers Gary Brightwell and Jashaun Corbin under contract.

The Saints led the NFL in rushing touchdowns (148) during Thomas’ tenure — largely because of Kamara’s development from a third-round draft pick into a five-time Pro Bowler.

Kamara became the kind of dual-threat the Giants want out of the backfield despite not figuring out how to tap into that part of Barkley’s skill set.

Thomas spent 13 seasons coaching running backs at the NCAA FBS level before joining the Saints, who twice ranked as high as No. 6 in rushing under his watch.