Chelsea have made contact with Sporting over a deal for defender Ousmane Diomande, as they explore centre-back reinforcements in January.
The 20-year-old Ivorian has been identified by Chelsea as one of their primary transfer targets, with striker options also being discussed internally.
Sporting have knocked back an initial enquiry from the Blues for Diomande, insisting they will only sell him for his full £69million (€80m) release clause.
Diomande has been a virtual ever-present for Sporting since joining from FC Midtjylland last January, helping them to the top of the Portuguese table ahead of rivals Benfica and Porto.
His former club Midtjylland is owed 20 per cent of any profit Sporting make from a future transfer, further complicating attempts to reduce the fee.
Chelsea want to sign another young central defender despite having Levi Colwill, Benoit Badiashile, Axel Disasi, Wesley Fofana, Trevoh Chalobah and Thiago Silva on the books.
Fofana is out with a long-term knee injury. Chalobah is available for sale in January to help fund new purchases. Silva could leave when his contract expires next summer.
Chelsea have also enquired over a deal for Sporting striker Viktor Gyokeres.
The former Brighton and Coventry City target man has 17 goals and eight assists in 20 matches in his first season at Sporting.
Sporting are again reluctant to sell their star forward and have demanded interested clubs pay his full £87million (€100m) release clause.
Chelsea have alternative forward options, including Napoli’s Victor Osimhen, Brentford’s Ivan Toney and Club Brugge’s Antonio Nusa.
Mauricio Pochettino may also enter the market for a midfielder, but that is considered a lower priority than signing a forward or a defender.
Pochettino could use 19-year-old midfielder Andrey Santos instead, as he is expected to be recalled from his disappointing loan spell at Nottingham Forest.
