US women's star midfielder Megan Rapinoe has suffered a torn right knee ligament during training and will undergo surgery with hope of returning in time for the Rio Olympics.

The 30-year-old from Seattle suffered a torn anterior cruciate ligament in a non-contact incident in Honolulu, an MRI exam disclosed.

Rapinoe helped the Americans win the Women's World Cup earlier this year in Canada and was a finalist for FIFA Women's World Player of the Year. She scored two goals in an opening-match victory over Australia to spark the US title run.

"I want to thank my teammates and the staff for the amazing support I've received so far," Rapinoe said. "I know I'll be in the best of hands moving forward and I'll be doing everything I can to get healthy as soon as possible.

"This is obviously a very difficult time, but I do feel super confident in my recovery as I've gone through this before and I know what the process will be like."

Rapinoe, who has 31 goals in 113 US caps, tore the same ligament in her left knee twice in college.

"She's certainly a major part of this team, both on and off the field, so to see her go down is tough," US coach Jill Ellis said.

"Megan has a great support system and she's very resilient, so we know she will be back as soon as possible.

"Players getting injured is always hard, but all of her teammates know that one of the strengths of this team is depth and everyone in the player pool is prepared to step up as we continue to prepare for Olympic qualifying."

The Americans are three-time defending Olympic women's football champions and have won four of the five Olympic women's finals contested, losing the other to Norway in 2000 at Sydney. They beat Japan 2-1 in the 2012 London Olympic final.