Goal understands both clubs sent delegates to watch the full-back during Nantes’ 1-0 defeat to Monaco on Saturday, as did a yet unconfirmed German team.
Kwateng played 90 minutes in the Ligue 1 clash, his 24th appearance in all competitions this season, and had to contend with the trickery of Rony Lopes and Georges-Kevin Nkoudou at Stade Louis II.
The full-back looks set to leave Nantes in the summer with his contract due to expire at the end of the current campaign. Talks are ongoing between the two parties about a new deal, which is now becoming increasingly less and less likely.
The 21-year-old plays predominately on the right of a back four but can also operate in the centre and at left-back.
Kwateng came through the youth system at Nantes and made his debut in August 2015. He has been capped at underage French level and was part of the side who won the Under-19 European Championships in 2016 alongside Kylian Mbappe.
His impressive showings now mean he has become a highly-coveted defender.
Southampton in particular are in need of a new right-back and lack depth in this area since allowing Cedric Soares to leave the club in January.
In his stead, their only natural right-back is Yan Valery, and James Ward-Prowse was even forced to take up that position in the Saints’ recent 1-1 draw with Burnley.
Watford too are are interested in signing Kwateng and see the Frenchman as competition for Daryl Janmaat. The Dutchman has established himself as first-choice right-back at Vicarage Road ahead of the likes of Kiko Femenia and Marc Navarro.
Kwateng follows in a long line of talented French full-backs to emerge from Ligue 1, with the likes of Mathieu Debuchy, Djibril Sidibe and Kenny Lala all currently operating in the France.
However, during last summer’s World Cup eventual winners France opted to play Benjamin Pavard in this position, although he naturally operates as a centre-back for his club side Stuttgart.