Former France international Nicolas Anelka is the club's only signing of the close-season so far, but Clarke is not concerned by the lack of new recruits.
"When you're chasing players you're always making enquiries, always speaking to people," he told the club's official website.
"It would be wrong for us to mention names, or comment on names. We are pursuing a number of targets.
"Now whether they fall into place tomorrow or next week, no-one can tell, so you have to be patient.
"At the moment, I'm not nervous because I know the people we have in mind.
"They are good, realistic targets who haven't gone anywhere else."