The midfielder was signed by Everton from SC Freiburg before the transfer deadline fell last week.
And Ball says Rohl has quickly impressed coaching staff as he's trained during the international break.
He said in his colum for the Liverpool Echo: "It can be frustrating for a manager – especially when you’re on form – when so many of his best players are away on international duty but working with a smaller group, you can have a proper, closer look at those who are still at Finch Farm.
"You can test them, you can drill them, and get a lot of information across more personally than with a much bigger group. The whispers I’ve heard is that Merlin has impressed and he’s adapted really well to the sessions and is impressing with his performances in training and that’s fantastic to hear he’s showing so much quality already as you don’t often get such glowing praise so soon."