The 20-year-old centre-back is very highly rated and played 20 matches in Ligue 2 last season.
Wolfsburg have already agreed a long-term contract with Lacroix himself, but need to reach an understanding with Sochaux.
The France under-20 international has told Sochaux bosses that he would like a move to the Bundesliga.
United made a €1m bid for the teenage defender, not enough to convince Sochaux.
And the Red Devils have yet to follow up on their initial offer.