Born in Haiti but raised in Belgium, he rose through the ranks of Anderlecht and represented his country at various age groups before appearing on his own for the Red Devils under Roberto Martinez in 2020.
He will provide competition for Ben Kabango and Harry Darling at Swansea, and could go straight to Williams' side at Norwich City on Saturday with Darling facing a potential three-match ban after being sent off against Sheffield United in midweek.
Swansea have appealed the decision to send off Darling, for his challenge on Rhian Brewster, and are waiting to hear whether the red card will be overturned.
Regardless of Darling's availability, Delcroix's arrival will bolster a Swansea side that has lacked depth in various positions all season.
Nelson Abbey provided central defensive support in the first half of the season, but his loan spell from Olympiacos ended at the start of January after the former Reading player made just one appearance for Swansea.
The Swans are yet to add to their squad this month, having failed to agree a deal with Wycombe Wanderers for Wales centre-back Jho Low.
