Ralph Hasenhuttl has already added two new faces this month in the form of goalkeepers Gavin Bazunu and Mateusz Lis, the former of whom joining from Manchester City for a fee which could rise to £15m.
According to The Athletic, the Saints are now closing in on their third signing, as they have agreed a €10m (£8.6m) fee with Bochum to recruit Bella-Kotchap.
The report adds that the 20-year-old is set to sign a four-year contract at St Mary's, with Southampton fending off competition from other Premier League clubs to win the race for his signature.
Bella-Kotchap has been a first-team regular for Bochum since they were promoted to the Bundesliga in 2020 and has made 49 top-flight appearances, including 22 last season.
The Germany Under-21 international's potential arrival would see him compete with fellow centre-backs Jan Bednarek, Mohammed Salisu, Lyanco and Jack Stephens for a place in Hasenhuttl's starting lineup.
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