Southampton are seeking a replacement for Jannik Vestergaard after his sale to Leicester City.
Fulham's Tosin Adarabioyo is one name being discussed, but Sky Sports News has been told free agent Gary Cahill is not currently an option, contrary to reports.
Like many other Premier League clubs, they have also been made aware of Ozan Kabak's availability for another loan from Schalke.
Ex-Manchester City academy graduate Adarabioyo is keen to return to Premier League football after impressing last season despite Fulham being relegated. Adarabioyo was statistically among the best performing centre-backs in the top-flight last term. Newcastle and Norwich have also made inquiries about him this summer.
Across 33 appearances, he made more interceptions per 90 minutes (6.56) than any of the other centre-back in the Premier League last season, according to Wyscout. He also made more successive defensive actions per90 (9.8) than Harry Maguire, and committed the second-least fouls per 90 behind John Stones.