Kenny Jackett has lifted the lid on his theory behind bringing triallists to Pompey.
The Blues boss revealed he often gets recommended players attached to no club and is open-minded when they arrive in pursuit of a contract.
Pompey have invited a number of free agents to train with the first-team squad since Jackett became manager in June.
The 55-year-old has cast his eye over Mohamed Maouche, Thomas Juel-Neilsen and Ceykan Karagozlu.
However, all three were unsuccessful in gaining a deal at Fratton Park.
Each failed to impress in matches for the reserves and were subsequently released.
Jackett often runs the rule over players who have been recommended to him as a way to build up a good rapport with contacts.
He feels he loses nothing having a look at them for a few days.
‘We get a recommendation off someone and then think if it’s worth viewing them in a game or part of a game,’ Jackett said.
‘The alternative sometimes is having them come in for a few days training.
‘It’s a recommendation from someone who we maybe want to keep in touch with.
‘If that’s the case then we feel it’s nothing lost on our behalf if we look at a certain level or situation. You do need some sort of filter system.
‘You can end up having a conveyor belt coming in and then you can’t see the wood from the trees.
‘But the principle is about being open-minded and hopefully you can turn one out.’
Free-agent Victor Adeboyejo has also been training with Pompey at their Roko base.
The Nigerian left Leyton Orient this summer after they were relegated to the National League.
Adeboyejo, 19, has also played two trial matches for Chelsea under-23s, while Bolton Wanderers and Barnsley are interested in the striker.
When assessing free agents, Jackett scrutinises if they will be a good addition to the first team – whether that’s at present or in the future.
The Blues manager also reiterated he is happy to delve into the free agent and non-league market as long as the players improve his current squad.
‘First off, you look at their physical profile, whether they’re good enough to be pros and go forward,’ Jackett added.
‘Secondly, you assess ability and align it to their attitude.
‘It’s about being open-minde. We do look at what’s out there and want to be unearthing a gem if we can and improve them.
‘I don’t really mind where they come from.
‘Good players make you a good manager and that’s it.
‘Whether I have brought them in, they were already at the club, if they’ve come from the youth policy or if they’ve come from non-league, I don’t really mind.
‘We want to make our playing squad as good as possible and that’s the job.’