The Blues forward has completed his much anticipated move to League One Fleetwood for an undisclosed fee.
It ends his two-and-a-half year stay at Fratton Park, where he scored 20 goals in 84 appearances.
Harrison had also been linked with a return to Bristol Rovers and Shrewsbury in this transfer window.
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However, he has opted for a move to Fleetwood and a reunion with on-loan Pompey right-back Callum Johnson.
That makes the 27-year-old Stephen Crainey’s first signing this month and follows the £1m departure of defender James Hill to Bournemouth and striker Callum Morton’s return to parent club West Brom.
And there’s been no hanging around, with the front man named in the starting XI for the Cod Army’s League One trip to Doncaster, which is only his second in the division this season.
Harrison’s Fratton Park exit will now allow Danny Cowley to step up his recruitment drive, with the Pompey boss operating on a one in, one out basis.
A new striker, along with a right-side centre-back, are his priorities this month – while, ideally, the Blues manager would like to freshen up his squad with at least four new recruits.
Cowley’s tasked will have been made a lot easier after it was confirmed earlier on Saturday that Haji Mnoga had joined National League Weymouth on a youth loan until the end of the season.
Meanwhile, he said after Friday night’s 3-2 Papa John’s Trophy win at Exeter that Gassan Ahadme was on the verge of leaving Fratton Park.
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