Will Ferrell "hobbled off the field" at a celebrity charity soccer match in May.
The funnyman was not laughing after he injured himself at the benefit.
According to British newspaper The Sun, Will was dismayed to discover that his athletic skills were worse than he imagined.
"They told me to have some laughs but everyone there has played semi-professional soccer," he explained. "I popped my hamstring and had to hobble off the field."
Will found little sympathy in others after tottering to the sidelines.
His team's coach thought it was laughable.
"The coach said, Hey Will, I saw you hobbling off and wondered if you were auditioning for one of your cowboy movies'," he joked.
"Then he laughed and just walked away."
The soccer match raised more than 4 million for Unicef.
Will's new political satire The Campaign also starring Zach Galifianakis will be released in US theatres August 10.