US national team coach Jurgen Klinsmann says his players need to place a greater emphasis on fitness as they build towards Sunday's friendly against Panama and hope to end an alarming run of three successive defeats.

Since defeating Ghana 2-1 in their opening match of last year's World Cup finals, beating a team that had eliminated them from the previous two World Cups, the Americans have only won once in nine matches.

The US squad will face Panama in suburban Los Angeles aiming to put an end to the run of defeats, the last one coming last week when classy South American outfit Chile beat them 3-2 and which stretched their run without a win to five.

Klinsmann says better form in the months after a World Cup is important for any team with designs on becoming a championship contender.

"Tension drops after the World Cup. I think all of the teams go through that," said the 50-year-old German, who has been in charge of the national side since 2011.

"But I think the more experienced teams, the teams that have far more peer pressure in their environment, they maybe allow themselves to drop 10 or 20 percent and not 30 or 50 percent. That is the difference to what we deal with."

Late goals saw the US held to draws last October with Honduras and Ecuador. Last week Chile scored twice in the final 25 minutes to secure a come from behind win.

While European-based players are at the heart of the 2014-15 campaign, those in the MLS are presently in their off-season and at their lowest fitness levels ahead of the new season which gets underway in March.

"It's difficult for me now to get them out of vacation. Some of them played their last game in October," Klinsmann said.

"I want to help them get back into shape, get back into rhythm. Some learned over time and prepared themselves really well and some don't have that knowledge yet.

"The culture is not there. They've got all the material. They should have done that (working out) twice a day, but reality is still different. It's just where we are right now, and we want to keep improving."