Allyson Felix of the US celebrates after winning the women's 400 metres event at the Golden Gala IAAF Diamond League at the Olympic stadium in Rome May 26, 2011. [Photo/Agencies]

EUGENE, Oregon - Three-times 200 metres world champion Allyson Felix will run the 400 metres at this weekend's US championships and her performance will help determine whether she attempts a 200m/400m double at August's world championships, her manager said on Monday.

"This is the next step toward deciding if she is going to do the double," Wes Felix told Reuters in a telephone interview. "It doesn't mean she will do it for sure ... but she would have to make the US team in the 400 to be able to double."

Felix has a bye for the 200 at the Daegu, South Korea, worlds as the defending champion but would need to finish among the top three in the 400 at the U.S. nationals to gain a spot on the American world team.

Her coach, Bob Kersee, told Reuters last month he was leaning toward Felix just running the 200 at the world championships. But Wes Felix said Kersee eventually left the decision to Allyson.

"She feels confident to be able to run at 400 metres, but running rounds (in the event) are a whole new thing for her," Wes Felix said. "So she is going to use the U.S. championships to see what three rounds of the 400 feels like."

Felix has the fastest 400 metres time in the world this season at 49.81 seconds, but the race will not be an easy one as 2009 world outdoor champion Sanya Richards-Ross and 2010 world indoor gold medalist Debbie Dunn will be in the race.

Americans Francena McCorory and Natasha Hastings also could be contenders.

Should Felix make the team, she likely will not decide until late July or early August whether to double or just defend her 200 title and run on the U.S. relay teams at Daegu.

"She is going to run a 200 metres race in Monaco on July 22 and that will be a great way to judge and see where she is at," Wes Felix said.