The 19-year-old Brazilian is one of the most sought-after players in the world.

Andre Villas-Boas will face his first major test as Chelsea manager after the Brazilian club Santos granted both Real Madrid and the Stamford Bridge club permission to speak with Neymar.

Santos president Luis Alvaro Ribeiro confirmed on Tuesday that five European clubs have met the buy-out clause of £40m in the 19-year-old's contract.

Chelsea owner Roman Abramovich will now attempt to see off rival interest -- believed to come from Real Madrid, Barcelona, Juventus and Russian club Anzhi Makhachkala.

It means that Villas-Boas faces going head-to-head with his former mentor Jose Mourinho for the player's signature.

Ribeiro said, "We did not want to sell Neymar but there is a contractual clause of £40m.

"Five of the most important European clubs offered to meet that clause. They asked to speak to the player and we have given them permission."

The Brazilian international is thought to favour a move to Real Madrid, but a Chelsea source told the Sun, "We have been after Neymar for a long time and remain confident we can bring him to Stamford Bridge."

The Stamford Bridge outfit are also monitoring developments with Sergio Aguero after it was revealed his advisers held talks with Atletico Madrid to reduce his release clause to £32m, according to the Daily Mail.

The Argentina international is eager to leave Madrid after another mediocre campaign but his current release clause of £42m has put off potential bids so far.

Reports have suggested that Juventus are the only club who could meet Aguero's current valuation but a drop in his transfer fee might persuade Chelsea and Real Madrid to table offers for the 23-year-old

If Chelsea do recruit another striker, Villas-Boas faces a potential headache over Didier Drogba's future at the club.

Reports in the morning papers linked the Cote d'Ivore international with a move to former-club Marseille with club president Vincent Labrune suggesting the club would be willing to bring Drogba back to the south of France.

"The question is whether in terms of salary Marseille have the means for four years to pay Didier Drogba," Labrune said. "I answer 'yes'. But we cannot afford 11 Didier Drogbas."

But Chelsea are reluctant to see the veteran striker leave and intend to open talks with the Ivorian aimed at extending his stay at Stamford Bridge, according to the Guardian.

Regardless of Chelsea's success in the summer transfer market, Drogba is still considered a vital component of the squad and the club intend to offer him a one-year extension on his current deal which expires next summer.