The pair are likely to share the pitch tomorrow night.
"I keep in touch with Mason quite a bit, I see him with England Under-21s now," McNeil said of Greenwood to the Manchester Evening News.
"He's doing well, he's a great goalscorer, you could see that growing up. He's a good lad as well, he's doing really well.
"United is about bringing young players through and giving them the game time, it shows they're still producing youth players, which is good to see."