Kevin Keegan was facing frustration in the transfer market last night with Pablo Aimar close to completing a £6 million move from Real Zaragoza to Benfica. Newcastle United, who have also had a £3 million bid for Stephen Warnock rejected by Blackburn Rovers, made a late attempt to lure the Argentina international to St James’ Park, agreeing a fee with the relegated Spanish club, but without success.

Given that Newcastle were expecting to open negotiations over personal terms with Aimar’s representatives later this week, the sense of disappointment on Tyneside will be sharp. While the 28-year-old’s physique may be slender, “The Little Clown” has been capped 51 times by his country and was hailed by Maradona as “the only current footballer I’d pay to watch”.

This summer, Newcastle have added only Jonás Gutiérrez, the Argentina winger, and Danny Guthrie, the former Liverpool midfield player, to a squad that Steve Harper, the goalkeeper, yesterday described as “depleted”. They lost out to Tottenham Hotspur for Luka Modric, the Croatia midfield player, while bids for Bafétimbi Gomis, of St-Etienne, and Arda Turan, of Galatasaray, have failed.

While Aimar would not have fitted seamlessly into Mike Ashley’s profile for new signings — the club’s owner wants young, ambitious players with a resale value — Newcastle’s offer reflects the fact that Keegan’s side requires some ready-made quality. After trailing Andrei Arshavin, the Zenit St Petersburg and Russia forward, and Arda, whose prices soared after Euro 2008, Aimar represented an affordable alternative.

His arrival would have eased concerns among supporters about Ashley’s motivations — he admitted last week that he was seeking new investment for the club — and the effectiveness of a recruitment department over which Keegan apparently exerts limited influence.

Prodded by Newcastle’s intervention, Benfica dispatched Rui Costa, their director of football, to Zaragoza’s training camp a to seal a deal that had faltered in recent days. “I am going to Portugal with my family to start a new adventure,” Aimar said after bidding farewell to his team-mates. “I would like to thank Benfica, who came here and got me.” He has been offered a four-year contract, which he may sign today.

New additions, particularly in defence — Anton Ferdinand has opted to remain at West Ham United — are a priority. Keegan has identified left back as an area he wishes to strengthen and the club are expected to submit an improved bid for Warnock, who was a consistent performer at Ewood Park last season. The 26-year-old joined Blackburn from Liverpool for £1.5 million in January 2007.

“There are a lot of empty spaces, so it would be nice to see those filled up,” Harper said. “We’ve still got a few weeks to do that so hopefully a few new faces will give everyone a lift.

“Of course we want to see new arrivals. We were maybe two or three short last year, given the injuries we had, and we’ve lost three or four since then.

We’ve brought in an Argentinian international who will hopefully excite the fans and do a good job for us. I’m sure the manager and the people upstairs are working hard behind the scenes to bring in the people we need because new faces would give everyone, players and fans alike, a big lift.”

Like Michael Owen, Harper is nearing the end of his present deal and is keen to agree an extension. “This is the last year of my contract and when you’re a player you’re always wary and looking for security,” Harper said. “I’m not too worried, but I’d like it sorted out over the next few weeks and hopefully it will.”

Despite being linked with Arsenal, Obafemi Martins has reaffirmed his commitment to Newcastle, who have appointed Robbie Elliott, their former player, as strength and conditioning coach. “I really want to play for Newcastle,” the Nigeria striker said. “I really love the fans as well.”