Now he’s wary of the 25-year-old enjoying himself at his Fratton Park reunion.
The attacker has been rejuvenated since joining Lincoln last summer in a £40,000 deal, netting two goals in nine appearances.
The former Bromley man endured a largely frustrating three-and-a-half years on the south coast, despite occasional glimpses of his natural talent.
Mousinho revealed the player was keen to quit the Blues, while the club certainly didn’t stand in his way.
Now, following a June departure, Hackett returns to face the new League One leaders.
Mousinho told The News: ‘For whatever reason, Reeco wanted to move on, which was fine.
‘I think it was probably the right time for him and the right time for the football club. Sometimes you go somewhere else and can hit the ground running.
‘He possibly needed a fresh start. That happens a lot, players just need a new environment, a new start.
‘I still think Reeco put in plenty of good performances for us towards the back end of last season, there were some games where he was outstanding, but he didn’t quite get that consistency he needed.
‘So it’s a fresh start, a brand new club, a different role for him, a different emphasis of what he can do for the side – and it’s going to be good for him.
‘Last season we had meetings with all the boys a couple of days after we’d played Wycombe and Reeco indicated he thought it was best to have a fresh start. We tried to facilitate that.
‘We always knew there was a bit of interest in him in January and Lincoln were one of those clubs, so it was relatively straightforward.
‘If, for whatever reason, things work out elsewhere and you haven’t necessarily got the best out of somebody’s ability, it can be frustrating, but it’s one of those things.
‘I don’t know what had gone on before I arrived, but maybe the writing was slightly on the wall for Reeco and he wanted a fresh start anyway, which was absolutely fine.’
Recruited by Kenny Jackett in January 2020, Hackett went on to score 11 goals in 79 appearances.
However, during his time with Pompey there were loans at Bromley and Southend, while various injury issues impacted upon availability.
Mousinho added: ‘There was never any doubt about Reeco’s ability and everybody who saw him play could see that, that’s why he was brought to this club.
‘Yes we would have liked to have seen a bit more of it out there, hopefully we don't on Saturday, we know what he’s capable of.
‘He has already scored goals for Lincoln and also played a bit out of position, and up front quite a bit, but adapted really well.
‘Lincoln fans will be really happy with his start.’