Newcastle could turn their attentions to out-of-contract Willie Caballero, should their bid to land No 1 target Pepe Reina fail.
Reina's agent hit back at claims in the Italian media that his client had agreed terms on a deal at St James's Park.
Instead, Manuel Garcia Quilon claims the former Liverpool goalie is set to stay at Napoli, despite the fact Stadio San Paolo outfit are looking at signing a new keeper this summer.
"Pepe will stay at Napoli until the end of his contract," said Quilon following a meeting with Napoli president Aurelio De Laurentiis.
"Certain issues have nothing to do with what happens on the pitch and do not interest us.
"He is staying at Napoli until 2018."
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This is unlikely to deter Benitez from pursuing one of his most trusted generals from his days at Anfield, especially with Belgian Matz Sels likely to depart this summer.
And Reina's situation could quickly change, with his club in hot pursuit of Arsenal's Wojciech Szczęsny, who spent last season on loan at AS Roma last season.
But should United's chase of the 34-year-old fall flat, Manchester City keeper Caballero could be a viable, relatively cheap alternative as Benitez oversees a complete squad overhaul ahead of the Magpies return to the Premier League.
The former Boca Juniors, Malaga and Elche man is set to leave the Etihad at the end of the month on a free transfer.
Meanwhile, the Magpies could tie up a cut-price deal for former Arsenal and Tottenham Hotspur defensive target Florian Lejeune.
The 26-year-old, of Elche, is rumoured to be available for £8.7million.