The Baggies have made four signings since the end of last season, bringing in Diego Lugano and Nicolas Anelka on free transfers, while Scott Sinclair and Matej Vydra have signed season-long loan deals.
But Clarke told the press of his hopes for more: "Time is short. I'm getting nervous and I'm concerned we've left it too late, that we won't get the players in to improve the squad.
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"As a head coach – I'm not a manager with a budget, remember – it means the club have the final say. I can make recommendations but it's down to the club to bring in players. My job is to work with the players."
West Brom are without a win in the Premier League this season and have failed to score in their two matches, with Clarke aware of the benefit that more new faces could bring.
"We do need some help," he continued. "Scott Sinclair coming in was great as he gave the place a lift.
"It would be nice to get a couple of others in but, if we don't, we go with what we've got. It's a long way to go until January, so there will be no other solution. At this moment I am not confident about signing anybody."