The defending champions have lost three of their opening four games and lie bottom of the Western Conference.

Their latest loss was a 1-0 defeat to Sporting Kansas City at Livestrong Sporting Park on Saturday and Arena said his team had been outmuscled by the home side.

"I think Sporting played well today. It was a very physical game. They really, on the day, did a better job in the battling department," Arena said.

"They beat us on every header today did a great job on second balls and I think over 90 minutes those are tough battles to lose and to their credit today they won most of them.

"I think their centre backs played very well in the box; they did a very good job."

Arena defended the performance of midfielder Landon Donovan, who made his first appearance in almost three weeks after a thigh strain.

"I thought Landon had a solid game today, he's been out for a few weeks, and usually the first game back isn't easy," Arena said.