The former Manchester United midfielder marked his full Hammers debut - 18 months after leaving Old Trafford - with a stunning goal in the 2-1 Capital One Cup win over Cheltenham.
Collecting the ball on the edge of the area just 40 seconds into the second half, Morrison turned inside, then out, leaving the entire Cheltenham defence wrong-footed before curling the ball low into the corner.
Morrison, 20, was once tipped as the finest talent to come out of the United Academy since Paul Scholes, but he left amid rumours of ill-discipline and a poor attitude.
Hammers boss Sam Allardyce gave him one substitute appearance the season before last and promptly loaned him out to Birmingham last term - and a stint in the Championship appears to have done him the world of good.
McDonald revealed: "As a young kid coming from Manchester thinking he could walk into the team, it was a bit of a shock to him that he didn't.
"I think the penny has dropped now and he's come back a wiser young man and we look forward to him keeping knocking on the manager's door.
"Now he has to keep scoring, he has to keep the ball, his all-round performance has to be good and he has to be consistent."