Barcelona goalkeeper Jasper Cillessen has emerged as one of Manchester United's primary targets if David de Gea leaves the club this summer.
The Spaniard has just one year to run on his contract, and he is yet to agree on fresh terms amid concerns over his wage demands. As it stands, he could leave the club for free next summer, with Paris Saint-Germain keen on signing him.
He said: "Problems with renewing his contract have got to a stage where Ed Woodward has informed the player that he will not meet the financial terms he's asking for to become the best paid player at the club, on the same level as Alexis Sanchez.
"What is definitely happening now is that Manchester United are looking for alternatives. They have started to look at the market and ask clubs for pricing on goalkeepers and to talk to the agents of those goalkeepers to see their interest in coming to Manchester United and what they would want in salary terms.
"One of the goalkeepers who is on that list of potential replacements is Jasper Cillessen, who is the second-choice goalkeeper at Barcelona. He transferred there from Ajax several years ago, at that point was regarded as one of the top young goalkeepers in European football, but has never fully managed to establish himself as first choice in Barcelona.
"He has a €60m release clause and two years left on his deal, but it's an indication of his status at Barcelona that Barca are asking for a €25m guaranteed payment, with performance-related bonuses on top."
Andy Mitten, editor of United fanzine United We Stand, told Sky Sports' Transfer Talk podcast that agents' fees are also proving to be problematic in keeping hold of de Gea.
He said: "The situation with David de Gea is that United have offered him a contract which would make him the best paid goalkeeper in the world and that is not enough. The agents' fees are alarming.
"I don't think United should be held to ransom just because they have this wealth. They are already overpaying for under-performing players. De Gea is not an under-performing player, he has been the player of the year for four of the last six years, but there are levels and he has been offered a deal to become the best paid goalkeeper in the world and it's not enough.
"I don't think United should just succumb to every agent's demands just because the fans are saying 'pay him whatever'. You can't just do that."