The Hammers, who are currently in 13th place in the table, welcome the former champions to Upton Park on Saturday.
Morrison believes that West Ham could beat City if they recreate the form that saw them defeat Tottenham Hotspur 3-0 in their last fixture.
"Of course we can cause a shock," he told the club's official website. "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."
Morrison scored two goals for England Under-21s on Tuesday during their 5-0 win over Lithuania in European Championship qualifying.