The 21-year-old joined on a season-long loan deal from Huddersfield but was injured during Pompey's League One opener against Rochdale on Saturday.
Manager Kenny Jackett confirmed the left-back's injury on Tuesday.
"It's not good news, it looks longer-term rather than short-term, which is a blow as he had a bright pre-season for us," Jackett told BBC Radio Solent.
Portsmouth loanee defender Tareiq Holmes-Dennis faces up to four months out with a knee injury.