Wimbledon champion Murray was beaten in straight sets in yesterday's quarter-final by Stanislas Wawrinka, but Becker expects the Scot to return to his best in the near future.
"He needs to set new goals, find new reasons to work harder and play better," Becker told BBC Sport.
"He hasn't been the number one player in the world, he hasn't won at the O2 [ATP World Tour Finals], he hasn't won the Australian Open.
"He's been playing so well for so long that eventually there's going to be a downer, eventually there's going to be a disappointment."
Murray is likely to lose ground on his rivals for the world number one spot after both Rafael Nadal and Novak Djokovic progressed to the semi-finals in New York.