The ex-Melbourne Victory defender has struggled to establish himself as a first-team player with Fulham and found himself in the English Championship with Norwich City who were relegated on the weekend.
Leijer will return to Craven Cottage where he will travel down under with the team in July but Merrick believes he may have to take a step back before he goes forward.
"To make the big time over there is not an easy task, you have to go through some very tough times before you make it," Merrick told AAP.
"I know Adrian and what he is capable of.
"I think he could play in the English Premier League, albeit that he might have to drop down to the Championship for a year. At the moment I think he's best staying over there."