Dave Coles believes John Sullivan has the ability to emerge from his Pompey set-backs and prove his worth.
And the outgoing coach has also been impressed with Trevor Carson and Phil Smith in the Blues’ goalkeeping pool.
The 49-year-old left Fratton Park on Monday after just under four weeks back at Pompey.
Working without a contract and claiming only expenses, Coles’ stay at the club he previously spent five years with was only expected to be a short one.
Nonetheless, he has had enough time to assess the credentials of the three keepers currently on club books.
Carson is currently number one although his loan is scheduled to end next month, while Smith is presently on loan at Dartford playing regularly.
As for Sullivan, he has not played for Pompey since the defeat at York at the end of September.
Yet the 25-year-old has made a favourable impression on Coles during his brief second stint with the Blues.
He said: ‘The three of them have had double sessions most of the weeks and done great, they have certainly responded to hard work.
‘John is a good goalkeeper and I am pretty sure that underneath there is ability waiting to come out.
‘Unfortunately I am not going to be around to squeeze it out of him but have loved working with him, he is a character and has the personality I like in a goalkeeper. David James had that personality.
‘He is not big and brash, he has a heart there that cares, and has a personality that actually fits the role of a goalkeeper.
‘That is the biggest thing for me, finding someone with a personality to deal with the highs, deal with the lows, deal with the mistakes. Mistakes come in different forms and it is how you deal with those.
‘John works hard but just needs to think more about his game and how he is going to get the things that he wants in his life, making them achievable.
‘He has done more work with me than the other two but that is because Trevor is playing so is the fittest goalkeeper at the moment and Phil won’t be far behind because he has been on loan at Dartford.
‘Sully is the one you have to make sure is prepared because he has been on the bench, so you need to keep pushing, pushing, pushing – and he has done well.’
Coles oversaw David James’ return to the England team and the emergence of Asmir Begovic during his first Pompey spell.
This is a very different club to the one he left for West Ham in the summer of 2010, but believes there is still talent there.
He added: ‘Trevor’s distribution is probably one of the best I have seen.
‘You talk about goalkeepers now having good distribution skills, he can kick off both feet and is a very natural kicker – as is John Sullivan.
‘He is a good shot stopper, very brave and also quick around the goal. He has a quick mind, sees danger, but is still young, so has time to develop.
‘Phil is very natural, a good technical goalkeeper, has good handling skills, has a nice manner about him and is very calm under pressure from what I have seen in training but I haven’t seen him in a game.
‘They are good guys to work for, have the club at heart and I have enjoyed it.’