Winger Antonio Valencia is destined to leave Wigan at the end of the season but is keeping his options open, according to his agent.
Diego Herrera claims Real Madrid have already lodged a bid - reported to be ¦pound;18million-plus - with the Latics but that there are other interested parties.
Herrera said with interest in his client from some of Europe's biggest clubs it was now difficult for him to stay at Wigan.
"Wigan revealed last week that there has been an offer from Real Madrid but they haven't told me any details about it," Herrera told PA Sport.
Manchester United are the other club regularly linked with the Ecuador international, who was signed initially on loan by former Wigan manager Paul Jewell in August 2006 from Villarreal before current boss Steve Bruce made the ¦pound;2million deal permanent in January last year.
Bruce has resigned himself to the fact the 23-year-old will leave in the summer but, as he did when Tottenham came in for midfielder Wilson Palacios in January, the Latics boss is determined to hold out for the best price.
Herrera added: "I don't know how much the offer is (from Real) and I haven't yet talked to anyone from Madrid about details of a contract so I don't know how long they would want him for.
"Wigan have not confirmed anything to me about Manchester United's interest.
"I know there are other clubs interested but as far as I know there's nothing official.
"I have yet to sit down with Antonio and see what he wants. We've not yet talked about which club he would prefer.
"Honestly I think it's really difficult that he remains at Wigan. I would anticipate that he leaves this summer. We have to see what will happen in the next few weeks. We're not in any rush."