Chelsea have a buy-back clause in the deal which saw Tino Livramento sold to Southampton.
The Sun says the club inserted a £40million buy back clause in Tino Livramento's Southampton contract.
Thomas Tuchel's side sold the right-back, 18, to the Saints for just £5m in August and he impressed against his former club on Saturday.
Livramento has been a regular under Ralph Hasenhuttl since joining Southampton, featuring in all seven Prem games this term.
The youngster had made just four professional appearances before moving to St Mary's - and they all came for Chelsea's U23s in the EFL Trophy.
The Croydon-born star is eligible to play for Portugal but has represented England at U15, U16, U17, U18, U19 and U21 levels.