22-year-old winger Josh Martin joins Pompey on a short-term deal until the middle of January.
The former Norwich City player, who left Carrow Road following the expiration of his contract at the end of last season, has been training with Portsmouth FC for the last few weeks.
Until now, head coach John Mousinho had advised that there were no plans to recruit Martin as a Blues player, however today that has all changed.
The gaffer told club media officials: "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 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."
The former Arsenal academy product has also spent time on loan at MK Dons, Doncaster Rovers and Barnsley and was on the scoresheet on 3 occasions across 23 games for The Tykes last campaign.
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