Gaine will be returning to the Texans, where he worked for three seasons as director of pro personnel and director of player personnel under general manager Rick Smith before leaving for Buffalo.
Smith has taken an extended leave of absence to be with his wife, who has breast cancer.
Gaine's extensive experience includes working in scouting and personnel since 1999. He started with the New York Jets, and five years later he moved on to work with the Dallas Cowboys from 2005 to 2007 and then with the Miami Dolphins from 2008 to 2013.
This past season, the Texans were well out of the playoffs with a 4-12 record. They were hurt when quarterback Deshaun Watson was sidelined with a torn ACL.
The Houston Chronicle reported that the Texans are also hoping to wrap up an extension for coach Bill O'Brien, who has one year remaining on his contract.
The Texans' coaching staff will be busy this month, coaching at the Senior Bowl game.