The club are hopeful that terms can be agreed with the 28-year-old's agents – expected on Tyneside today – over the next 48 hours.

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North-east rivals Sunderland are also understood to be interested in the Argentina international, as well as Portsmouth and Benfica.

But Newcastle are now in pole position to sign Aimar.

Should Aimar join United, he would be the second Argentine at the club, with Kevin Keegan having already signed winger Jonas Gutierrez from Real Mallorca.

And, as revealed in yesterday's Echo, he also has an interest in signing Liverpool's Argentina Under-20 international Emiliano Insua. But this proposed capture would be the club's biggest coup, with the attack-minded Aimar the kind of player Keegan loves to work with.

Aimar has struggled for form at Zaragoza, but Keegan believes he can get him playing the kind of football which earned him a reputation as one of his country's brighest stars during his time at Valencia, where he won a UEFA Cup winner's medal.

Meanwhile, Newcastle have failed in a bid to sign West Ham United's Anton Ferdinand, with the defender making it clear he wants to stay at Upton Park.