The 20-year-old striker Ma first tore the ligament in December last year and only returned to action in June. She has been compared to Rooney both for her talent on the field and temper off it.
In 2006, Ma was the first female to win the Asian Youth Player of the Year award. But she was almost kicked off China's team at the 2006 U-20 Women's World Cup for attitude problems. She later drew headlines when she complained about the terms of her contract with her club Dalian Shide.
Ma is the second Chinese to be seriously injured in tune-up games. Qu Feifeibroke her leg in a match against New Zealand
China, which will open its Olympic campaign against Sweden, is coming off a tumultuous year during which it has had two well-known foreign coaches come and go.
Former coach Shang Ruihua took over the Steel Roses in April after Frenchwoman Elisabeth Loisel departed after only six months in charge.
Loisel, who complained of interference from Chinese federation officials, did not return to China after the Steel Roses finished ninth out of 12 teams at the Algarve Cup in Portugal.
Loisel succeeded Swede Marika Domanski-Lyfors, who left following China's quarterfinal finish at the 2007 Women's World Cup. (Domanski-Lyfors' assistant was current U.S. coach Pia Sundhage.)