The Mail on Sunday says West Ham make a £25,000 payment to Manchester United every time the midfielder makes a first-team appearance.
The Hammers agreed the deal as part of the complicated transfer that sent Morrison to Upton Park last year on top of the initial £650,000 fee.
Morrison has so far made eight appearances for West Ham this season - triggering payments of £200,000 to United - having spent the previous campaign on loan to Birmingham City.
When Sir Alex Ferguson decided to sell Morrison in January of last year, a £3m fee was discussed with West Ham.
But the London club eventually paid a fraction of the figure that was initially demanded upfront and instead agreed to pay United per game.
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