Morrison made his debut at U21 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."
Wilfried Zaha is expected to come into the side in Sterling's absence and Southgate does not see any difference in his confidence despite not having played a Premier League game for new club Manchester United since his move from Crystal Palace.
"It is tough for him," Southgate said. "It is tough for any player when they are not playing regularly. Wilf has joined a new club with all the difficulties that brings.
"But it was never my intention to play him in both of our matches this week. He understood that. But he has got the opportunity now to show people what he is capable of.
"Have I noticed a lack of confidence in him? No. There is probably some frustration because he just wants to play.
"But he is at a fantastic club and he realises that to get in the team is going to take a lot of work and patience."