Despite interest from some of Europe's top clubs, the former Corinthians pair chose to join English Premiership minnows West Ham.

Since then, several details and murky rumours about the transfers have emerged in the British press, leaving UEFA admitting they are worried about the situation surrounding two players seemingly owned by an investment group rather than a club.

"The West Ham situation concerns us, whether regarding the identity of the eventual owners of the club or the case of Tevez and Mascherano, because we don't know who owns their registration," UEFA spokesman William Gaillard told AFP.

According to the British press, the two players, who had been touted around some of Europe's top clubs, are owned by Media Sports Investment (MSI), a group which also holds a majority stake in Brazilian club Corinthians.

One of MSI's owners, Iranian-born Kia Joorabchian, is also among a consortium of businessmen believed to be involved in a secretive takeover attempt at West Ham.

"This concerns us. But I don't think the British government can do anything and neither can we," added Gaillard.

The news has sparked FIFA into a quick rethink of its regulations and world football's governing body said Sunday it would try to invoke new rules forcing individuals trying to take over clubs to reveal their identities.

According to the British press, West Ham are only paying half of the two players' wages, with the other half being picked up by MSI, who paid a combined 35 million dollars for the pair in 2004 to take them from Argentina to Brazil.

MSI retained the players' registrations and when they left Corinthians, the Sao Paulo club received nothing and West Ham paid nothing.

"Theoretically there are no rules outlawing it," said Gaillard when asked if there was anything wrong with an investment company owning players' registrations.

"The players maybe have a problem in knowing who owns their contracts. If they don't have a contract with West Ham but have one with MSI. But we still don't know, we're in the dark.

"Right now, no-one can do anything and that's what's alarming. Nothing is stopping anonymous people owning clubs or even players.

"We don't know if these players are owned by others, but this idea is still serious."