Valencia is currently absent from United's pre-season tour of North America with an ankle injury sustained while on international duty with Ecuador, but chief executive David Gill has revealed that the 25-year-old has accepted a long-term offer from the club.
"We are in the process of finalising that. Antonio has been away at the Copa America and we've been away here in the US, but that's broadly sorted out," Gill told the Daily Mail.
"Antonio initially signed for four years, so he's got two left. The length of the deal will come out as and when, but it's a longer-term deal.
"That should be announced next week, when we're back."