Lenny Stéphane Lacroix, born in Strasbourg, was formed at RC Strasbourg and FC Mulhouse before joining the academy of FC Metz. A right-footed centre-back who can also fill in at right-back, he signed his first professional contract with Metz on 18 December 2019 and made his Ligue 1 debut on 16 January 2022 in a 1-0 win over Reims.

Benfica recruited him on 3 August 2022, announcing him as a reinforcement for the B team on a four-year contract. He arrived alongside a group of young signings brought in to strengthen the reserve side following Benfica B's Liga Portugal 2 campaign.

Through 2022/23 Lacroix played for Benfica B in Liga Portugal 2 under Luís Castro, gaining second-tier experience without progressing to Roger Schmidt's first team, which was building its central defence around Nicolás Otamendi, António Silva and Morato. He has represented France at under-16, under-17 and under-19 level. He later returned to French football with Dijon FCO.