"Goran has to step up and show he can challenge for the left-back position again because Liam has been really good since he got back in," said Clarke.
"Liam's had a little chance of an extended run in the team and done well.
"I like to think all the players every week, every day are trying to impress me, but there is an end product for Goran.
"His situation won't be finalised until the end of the season and he has to keep at it, keep impressing and work every day in training.
"He's made some impressive performances for us and the type of competition we've got for the left-back position is the kind of competition you want to replicate all over the pitch."
Clarke feels the competition for places can only be a good thing for his players.
"There are two good players fighting for the same position.
"It focuses your mind if someone is trying to take your place and it works in reverse if you're trying to get into the team."