The German midfielder signed a short term deal with Everton on Friday after training with the Blues for several weeks.
But Moyes is keen to take an even closer look at the 30-year-old and doesn't expect the German to figure imminently in the first team.
The Everton manager said at his Friday press conference : "What we're going to do is see how he is first. We're not saying what he's going to bring to us - he may even come here and not play. We just want a longer period to have a look at him, make sure he's fit and see if he can offer us something.
"We're short on midfield players so we could do with another, but I couldn't turn around right now and say he's ready to play in the Premier League. But he's trained for four weeks - the equivalent of doing a pre-season."