Manchester United look to have received a boost in their reported attempts to sign Celtic’s Victor Wanyama with the news that the midfielder has rejected the Scottish champions’ offer of a new contract.

The 21-year-old has continued to impress since moving to Glasgow from Belgian side Beerschot in the summer of 2011 and is said to have turned down an offer from an unnamed Premier League club in the last transfer window.

While Wanyama has previously stated his desire to remain with Celtic, his refusal, to date, to extend his deal beyond 2015 throws his future into doubt.

"Victor informed Celtic the contract offer fell short of his expectations,” Wanyama’s agent Rob Moore told Scottish broadcaster STV.

"There were a number of aspects that fell short—he turned it down.

“He is very happy with the job he is doing at the moment,” he added. “He is a great professional and his commitment cannot be questioned.

"But it doesn't take a rocket scientist to work out that he lost great earning potential in the summer [by not moving to England]."

Celtic manager Neil Lennon appears unlikely to allow the Kenyan to leave on the cheap, however.

“£25m,” Lennon responded when asked to put a valuation on his charge, according to BBC Sport. “Wanyama has the world at his feet.

"But his feet are here and they won't be going anywhere unless we say so."

 Arsenal and Chelsea are also reported to be interested in the player.

Manchester United also look likely to have to pay a high price if they are to lure another of their reported targets to the club. Highly-rated Porto winger James Rodriguez has had a £38 million release clause inserted into his contract by the Portuguese club, according to TalkSport.

The move is likely to ensure that they can recoup a lofty fee for the 21-year-old Colombia international. United have been repeatedly linked to the player and Ferguson commented on the speculation this week.

"With regards to James Rodriguez, I hope the news is not true because it costs a fortune to sign a player from FC Porto,” he said.

Rodriguez could potentially be a long-term successor for Nani, who continues to be linked with a move away from Old Trafford. The Portuguese winger has less than two years left on his contract and reportedly priced himself out of a move to Zenit St Petersburg in the summer.

Nani has now given a cryptic response to a question about his future.

“Only God knows what awaits me," he told the Sun. "I am in perfect condition—I am physically good and feeling confident. I am the same Nani as always."

In other news, with there still uncertainty about the goalkeeping position at Old Trafford as Sir Alex Ferguson switches between David de Gea and Anders Lindegaard, Sunderland stopper Simon Mignolet has been discussed as a possible United target.

The Belgium international has said that he is aware of the speculation.

“I have even read it on the Internet,” he told Belgian publication Het Nieuwsblad. “I know nothing about it. Of course it's nice to be linked to such a large team but I'm happy at Sunderland."