Foster out for six months
By Simon Fudge
Last Updated: 01/01/70 1:00am
The 20-year-old suffered the injury while playing tennis and Foster will need exploratory surgery to correct the problem.
He will most certainly miss the start of next season with the Britannia Stadium outfit, as Potters boss Tony Pulis faces the prospect of having a lack of cover in the custodial department.
"It's a big blow for Ben and for us," Stoke's director of football John Rudge told the club's official website.
"We were expecting him to make great strides this coming season and push forward.
"We will be assessing the situation."
Foster spent part of last season with non-league side Tiverton Town and Division Two outfit Bristol City but his chances of playing before the New Year - based on his initial diagnosis - seem slim.