Paul Downing has joined Rochdale on loan for the remainder of the 2021/22 campain.
The 30-year-old centre-back has made 27 appearances since arriving from Blackburn in the summer of 2019.
Blues boss Danny Cowley said: "Paul is an excellent professional and we wish him every success moving forward.
Rochdale currently sit 17th in League Two following their relegation last season and have not played since beating Newport 3-0 a week before Christmas.
Downing featured four times for Pompey this term, last appearing as a late substitute in November's win at Wycombe.