The Irons' 3-2 defeat at home to Newcastle on Saturday means Manuel Pellegrini's team are five games without a win.
"I think the way we started, from our point of view, just wasn't good enough," Cresswell told whufc.com. "Credit to Newcastle, they did well in the first half. But we can't go 3-0 down and then look for a reaction. We were chasing the game at 3-0.
"The last 15 minutes or so was ours with Newcastle dropping deep. All teams go through tough patches and we are in one at the minute. We've got to put that right and start again on Monday.
"It's not good enough. We spoke about set-pieces before the game and yet, to concede them, wasn't good enough. We need to go through it. We're going through a bad period and we need to stick together."
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