John Sullivan has joined Cambridge United until the end of the season.
The keeper has moved to the Skrill Premier outfit after being linked with a switch to Abbey Stadium over the weekend.
Sullivan will link up with former Pompey defender, Richard Money, who is manager at the Us.
The 25-year-old arrived from Charlton over the summer on a two-year-deal.
But Sullivan has found himself down the pecking order after Trevor Carson arrived from Bury.
He made seven appearances this season for Pompey.