He is relishing Saturday's Barclays Premier League visit of Manchester City.
Morrison told West Ham TV: "I'm very excited because obviously I used to play for Manchester United but I never played against their first team so I'm really looking forward to it.
"Of course we can cause a shock. We're a great team and we should have had a lot of goals this season but for some reason we haven't.
"Against Tottenham we managed to get the goals which have been missing which was pleasing. The defence has been solid so if we carry on doing what we're doing we can cause an upset."
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