Alex Bass has joined Bradford on loan until the end of the 2021/22 season.
The 23-year-old keeper has made 41 senior appearances for Pompey, having progressed through the club’s academy.
Seven of those outings have occurred this season and include clean sheets in League One wins at Fleetwood and Wycombe.
Blues boss Danny Cowley said: “From the moment we arrived at the club, Alex has been an outstanding professional.
"It’s really important for him to go out and play regularly, so when this opportunity became available, we didn’t want to stand in Alex’s way."
“He always conducts himself to the highest standards, but had a really tough time with injury last season.
“Whenever he’s been called upon, his performances have been superb and we want to do the right thing for the player in the long-term.
“It’s really important for him to go out and play regularly, so when this opportunity became available, we didn’t want to stand in Alex’s way.
“We’ve got young Toby Steward and we are also looking to bring in another keeper in the near future.”
Bradford – whose squad includes former Fratton favourite Gareth Evans – currently sit 12th in League Two and drew 0-0 at Rochdale on Saturday.