Borussia Monchengladbach defender Jannik Vestergaard is a target for Southampton.
Sky Sports says Southampton are one of a number of Premier League clubs interested in Vestergaard.
Initial talks between the clubs have focused on trying to agree a transfer fee.
West Ham are also thought to be interested in the 25-year-old, who was part of Denmark's World Cup squad in Russia.
Saints boss Mark Hughes has already made two signings this summer, bringing in winger Mohamed Elyounoussi from Basel and midfielder Stuart Armstrong from Celtic.