The 32-year-old joined the Parkhead club at the end of the January transfer window on a short-term loan from Crystal Palace.
Schlupp has taken to life in Glasgow's east end like a duck to water, highly impressing with his performances so far.
He has now cemented his place at left-back in Brendan Rodgers' starting 11, although McCormack, from his experience of playing in the English leagues, doesn't think fans have seen Schlupp's versatility.
He said (Open Goal): "See, the big thing with him is from living down south for years and years, I watch a lot of football down there, the amount of positions he can play that Celtic fans and Scottish football fans haven’t seen yet.
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"He plays left winger, right winger, number ten, defensive midfield. But, you haven’t even seen him play anywhere near the level he has been playing at for years."
Given the level of his performances so far in green and white, question marks have been raised over whether Schlupp might make his move to Celtic permanent come the summer.
The Ghana international is out of contract at Selhurst Park in tandem with the season's end: "It’s an absolute no-brainer to sign him," said McCormack.
“People are saying he will have to take a wage cut. No, he’s not because he’s going to be on nothing anyway because he is out of contract. There is no wage cut. How is that a wage cut?
“You have to then take into account, unfortunately, the way Kieran Tierney is. He gets a lot of injuries. So, even if he [Schlupp] comes as a second-choice left-back for Celtic, he can still end up playing 20 games or whatever."