Rowe was hurt during the club's recent 6-0 friendly victory over St Neots Town.
The 23-year-old, manager Darren Ferguson's first choice left-back, will undergo a scan later this week to determine the full extent of the injury but the Posh boss already suspects bad news.
He said: "It's a shame for the lad as he's barely been injured since I've been here. We expect him to be back after the first international break (in September)."
Rowe has made 124 appearances for Peterborough since joining them from Stockport in May 2009.