The American international suffered the injury in Friday's 1-0 friendly win over Czech side Bohemians as Blackburn ended their tour of Germany.
Friedel had to be replaced by Peter Enckelman after just 23 minutes and he is set to miss the rest of Blackburn's pre-season build-up.
"The one downside of the night is we've lost our goalkeeper and I don't think he'll take part in too much of pre-season after that," said manager Graeme Souness.
"I think it's his kicking muscle at the top of his leg, which he's damaged before, so I don't think he'll play in the rest of our pre-season matches."
