Pompey have signed Josh Martin on a short-term deal until the middle of January.
The 22-year-old winger has been training with the club for the past few weeks following his departure from Norwich at the end of last season.
Blues boss John Mousinho said: “He’s done really well during his time with us and we know what qualities he can bring.
“We’ve had such a strong squad in that time, but circumstances have obviously changed with the injury to Tino Anjorin and we felt this was the right thing to do.
“Josh is an excellent player and actually had a couple of other options, but we’re delighted that he’s chosen to sign with us.
"He’s done really well during his time with us and we know what qualities he can bring."
“He’s pretty good with both feet and likes to drift inside, while he can also finish, so there’s plenty of excitement he can bring.
“Josh has got a lot of technical ability and has played in both the Premier League and Championship – we know we’ve got a good player on our hands if we can get him going again.”
Former Arsenal trainee Martin turned professional with Norwich and made 16 appearances for their first team.
Five of those came in the Premier League at the conclusion of the 2019/20 campaign, with outings against the likes of Chelsea and Manchester City.
He has also spent time on loan at MK Dons, Doncaster and Barnsley, netting three times in 23 games for the latter club last term.