SYDNEY (AP) — Two-time world swimming champion James Magnussen said Wednesday he is retiring after winning 15 medals for Australia at major international events over a 10-year career.

The 28-year-old Magnussen was affected by shoulder injuries over the past several years. He won world 100-meter freestyle titles at the 2011 and 2013 world championships in Shanghai and Barcelona, respectively.

In 2012 he won silver in the 100 freestyle at the London Olympics, touching .01 seconds behind gold medalist Nathan Adrian of the United States.

Following shoulder surgery in 2015, he returned to compete at the 2016 Rio Olympics where he won a bronze medal as part of the Australian 4x100 freestyle relay team.

"I have taken the time to make the best decision for myself moving forward and to do that I wanted to make sure I was in the best space mentally and physically before announcing my retirement," Magnussen said in a statement. "I believe now is the right time to step away from the sport."

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