Portsmouth boss details reasons behind ex-Sunderland and Millwall man's disappointing exit as he prepares for Fratton reunion

The popular attacker netted five goals in 17 appearances during the second half of last season after being a January deadline-day recruit from Sunderland.

However, despite a role Danny Cowley believes was ‘key’ in a Blues resurgence which brought just three defeats in their final 18 matches, O’Brien disappointingly departed the south coast.

The 29-year-old was desperate to remain with Pompey, while the club showed their hand by offering a fresh contract.

Yet the ex-Millwall man instead moved to Shrewsbury in July – and is now poised to return to Fratton Park with his latest club tomorrow.

Cowley told The News: ‘Aiden came in with a smile on his face every day, loves football, and we would have really liked to have been able to extend his stay here, but it wasn't possible.

‘It just wasn't possible, it didn't fit for either party, that’s just football sometimes. It just didn't quite work out, sometimes it’s finances, sometimes it’s the timing.

‘Let’s also not forget that Shrewsbury are a club that have been really aggressive with their recruitment this summer, don’t underestimate how many good players they've got at their club.

‘We would have liked to have been able to make it happen with Aiden, it wasn’t anybody's fault, but sometimes the timing isn’t right.

‘He was really important, not just as a player but as a person as well, he brought real energy and enthusiasm to the training ground and played a really key part in that run of 18 games.

‘I can remember him scoring late against Fleetwood, scoring against Wigan, his first touch against Doncaster, that run against Accrington when down to 10 men, and overall having a real impact.

‘I thought he did well for us, sometimes it’s a good fit. He had some really good moments – hopefully he doesn’t have any tomorrow.’

With O’Brien not returning to Fratton Park at the end of his contract, the Blues instead pursued other attacking options.

That brought Colby Bishop to Pompey, along with loan duo Dane Scarlett and Joe Pigott to bolster their firepower.

Cowley added: ‘We are pleased with the recruitment work we did this summer, we are better than we were this time last year, we are convinced of that.

‘We have some key injuries at the moment, which isn’t allowing us to have full disposal of the squad, which is mega frustrating, but this is the reality we are in.’