"I think the form of Shaun has been great, since the latter half of the last season he started to find his feet at the club and he started putting in some good performances. He's continued that, he had a great pre-season and he's in the team on merit," Clarke told Chelsea's website.
"He's one of our top performers and very consistent, it's good for Chelsea.
"With Shaun it was a long process, he was used to being the top guy at Manchester City, he was playing week in week out, without the same scrutiny on his performances.
"'When he first came here he had to perform from the bench in 20 minutes. He came on, didn't do very well and found himself out the team again."