The Ecuador winger is halfway through the four-year deal he signed after arriving from Wigan for ?16million in June 2009. United are prepared to improve Valencia's ?50,000-a-week contract but early discussions faltered when his representatives asked for image rights to be included in the new package.
Snag: Antonio Valencia's Man United deal has stalled over image rights
Old Trafford chief executive David Gill is refusing to agree to image rights clauses while investigations continue by HM Revenue and Customs, who believe they may be able to recoup millions owed in tax on the payments across the Premier League.
United are still optimistic they will reach a compromise with Valencia, 25, who has been one of their most impressive performers after recovering from the serious ankle injury he suffered in September.
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Explore more:People: Antonio Valencia, David Gill Places: Ecuador