Sky Sports sources understand that Chelsea have made a bid for Porto midfielder Alvaro Pereira.
Blues boss Andre Villas-Boas worked with the 25-year-old Uruguay international before he joined the Premier League side this summer.
But it is now believed that Pereira could be following his former coach to Stamford Bridge, with the London club looking to replace Yuri Zhirkov who has joined Russian outfit FC Anzhi Makhachkala.
Pereira would fill that void after gaining a reputation as a highly rated wing-back.
Chelsea are the highest spenders of all 20 Premier League clubs this summer, with Juan Mata the latest signing, joining from Valencia for £26m.
Pereira began his career in Uruguay with Miremar Misiones and spent time at Quilmes and Argentinos Juniors before moving to Europe to play for Romanian side CFR Cluj.
He made the move to Porto in 2009 and played a significant part in their treble winning side under Villas-Boas last year.
It is understood that Pereira has a £25m release clause.