The pair played for Jürgen Klopp's side in a behind-closed-door friendly against Blackburn at Anfield earlier in the week, with Clarkson completing the 6-0 win by scoring an eye-catching goal.
McManaman told LFCTV: “When I see some of the players who are excelling at the Academy, there's nothing better than not seeing them again.
“I mean that in the nicest way because they move up to Melwood, and I love it when I don't see them again because it means they're at Melwood and they're excelling at Melwood.
“There's nothing better for these younger players with talent to play with better players, to play with players who are at the top of the game.
“If you've got anything about yourself and if you want to be a first-team player in the future, you should be able to improve so much by playing with the best players in the world – and that's who Liverpool have got at the moment.
“I love the fact that Leighton and Jake are there, Neco Williams is there and Curtis has, of course, been there a while, like a number of the older ones. But whenever they disappear to Melwood and hold their own, that means they're improving, that means they're getting better."