Birmingham City captain Damien Johnson will miss their opening game of the Premier League season at Chelsea.
The midfielder, 28, suffered a tear of his hamstring in July's 2-0 friendly win against Walsall.
Johnson will also miss the home game against Sunderland, but is aiming to return for the match at St Andrews against West Ham on Saturday 18 August.
"Jonty will be out for a total of around 21 days from the time he did the injury," confirmed manager Steve Bruce.