Mauricio Pochettino expects to be at Southampton next season and is looking forward to working with chairman Ralph Krueger.
Loan pair Sam Hutchinson and Leon Best have extended their deals at Sheffield Wednesday.
The Montbeliard-born striker returns to the club where he began his career after impressing manager Herve Renard on trial following his exit from Qatari club Al-Wakrah.
The 33-year-old helped guide Sochaux to promotion in 2001 but now faces the challenge of attempting to lift them off the foot of the Ligue 1 table.
"I want to come back to lend a hand," he told L'Equipe.
"This is where I was born, where I started, it is a homecoming.
"Late last week, the coach told me he had been reassured by my physical condition.
"Although, initially, I wanted to wait until January and not rush, I did not hesitate."