Haji Mnoga has put pen to paper on a new three-year contract at Fratton Park.
And the 19-year-old defender will now be looking to gain more first team experience after joining Bromley on loan until January.
The National League club – who sold Liam Vincent to Pompey earlier in the summer – are 10th in the table after collecting three points from their opening two games.
Blues boss Danny Cowley said: “We’re delighted to extend the contract of an incredibly exciting young player, who possesses fantastic athleticism and power.
“He’s also got a real eagerness to learn and get better – which are qualities we like to see in any young player.
“Trying to find the right pathway for Haji has been really crucial, although the selfish part of me wanted to keep him with us because he drives the intensity in training every day.
“But we’ve ultimately taken a longer-term view, which we feel is best for both him and this football club.
“He’s gone to a Bromley side, who – in Alan Dunne and Roger Johnson – have two really good defenders as part of their coaching staff.
"We’re delighted to extend the contract of an incredibly exciting young player, who possesses fantastic athleticism and power."
“They also have a good record in recent years of developing young players, including Reeco and Liam.
“It’s a good fit for us and our relationship with the club will allow him to maybe come back and be involved in some of our Papa John’s Trophy games.
“He’ll be able to train with us at times and it’s important that we also keep a handle on his development.
“Young players need good coaching, but they also need a challenging games programme – and that’s what this move will provide.
“So we’re delighted to create this pathway for him and we’re really looking forward to seeing his progress.
“The academy have done a really good job with him and when they can see one of their own coming through, that can be a really powerful and inspiring thing for all our young players.”
Academy graduate Mnoga made his senior Pompey debut in a 2018 EFL Trophy group stage victory at Crawley.
He has appeared 13 times for the club and opened his goalscoring account at Cheltenham in the same competition last season.