Morrison made his debut at Under-21 level in the 4-0 win over San Marino last week only a few days after his starring role in West Ham's surprise 3-0 victory over Spurs at White Hart Lane.
He is part of the exciting attacking talent at Southgate's disposal and should start again, with Raheem Sterling having joined up with Roy Hodgson's senior squad for the clash with Poland.
"Well, he's a different type of player to the others that we've got here. He's capable of things that are very, very different, there's no question about that, and it's exciting to watch," Southgate said.
"We're a squad with lots of exciting players and I don't want to heap all of that focus on to one. I want him to be able to go on the field and express himself."