Chelsea have offered Spanish side Atletico Madrid nearly 50 million euros for their Argentine international striker Sergio Aguero, a newspaper reported on Saturday.
The English Premiership side would be willing to pay Atletico up to 57 million euros if the deal included another Argentine player, Maxi Rodriguez, sports daily Marca said.
Atletico has consistently said that it does not want to let Aguero go.
The 21-year-old son-in-law of Argentina manager Diego Maradona has a recision clause in his contract with Atletico worth 60 million euros.
He joined Atletico in 2006 from Argentine side Independiente and is under contract with the Spanish team until 2012.
Aguero scored in Argentina's 3-2 friendly victory over Russia on Wednesday.
If he plays for Atletico during the club's Champions League qualifier against Panathinaikos next week he will not be able to play in a European competition for any other side this season.