David Moyes has warned Manchester United that Declan Rice will cost more than £100m next summer.
The England international was linked with a move to Old Trafford throughout the summer.
Many United fans expected the club to bolster their midfield options, but the arrivals were in other areas of the pitch.
West Ham had previously slapped a £100m asking price on Rice, who has continued his excellent form at the start of this season.
The 22-year-old helped Moyes' men to a 1-0 victory over Tottenham on Sunday, as the Hammers rose to fourth place in the Premier League table.
He has played every minute of every game in the top flight and has also excelled in continental competition, where West Ham have won three games out of three in the Europa League.
United are expected to bring a midfielder to Old Trafford next summer, with Rice thought to be one of their top targets.
But Moyes has now revealed that West Ham have raised their asking price for one of their prized assets.
"There was a bargain to be got [in the summer] with Declan at £100million. That bargain has now gone," he told Sky Sports.
"We have a lot of really good players at this football club and I think while you're building and developing I think people might always come and look at your players.
"But it is good that they are because that is telling us that they're doing well."
West Ham's desire to keep hold of Rice is understandable; the midfielder has been one of the Premier League's standout performers so far this season.
They are not under any immediate pressure to sell either, with Rice under contract at the London Stadium until 2024.
West Ham also have an option to unilaterally extend his deal by an additional 12 months.
Manchester United would therefore need to pay a substantial sum to prise the England international away from his current club.
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