That will include new-boy Liam Vincent, who is deemed to be one for the future, and Reeco Hackett-Fairchild, who spent a largely uneventful loan spell at Southend last season.
But with Ronan Curtis also attracting interest and Pompey open to offers for players, that figure could easily drop as Danny Cowley overhauls the playing squad he inherited from Kenny Jackett.
With that in mind, we look at those 13 players who are currently contracted to the Blues and assess what their futures might hold.
1. Alex Bass - goalkeeper
The keeper served as Craig MacGillivray's understudy all last term - bar the nightmare season-opener against Stevenage, which eventually saw the Scot emerge as the Blues' penalty shootout hero. Bass has the chance of redemption, though, with MacGillivray gone and the 23-year-old already highly-rated by the new head coach. Competition will arrive but expect Bass to start the first game of the season.
2. James Bolton - right-back/centre-half
An honest and reliable performer, six of Bolton's 13 league appearances last season came after Danny Cowley arrived in March. Two of them were starts, but you get the feeling he'd be allowed to leave if an offer came in. Game perhaps doesn't suit the Cowleys' way of playing. Is one of the 2019 summer recruits that has never hit the heights expected of him.
3. Lee Brown - left-back
Liam Vincent has already arrived this summer to provide competition at left-back and another new addition for that position is expected. Cowley knows already, however, that Brown is a reliable and effective performer at this level and will do a decent job for him. As always, though, every player has his price - and the bumper new deal the defender signed last summer might help free up extra room in the budget.
4. Ronan Curtis - left-winger/forward
The Republic of Ireland international has made no secret of his desire to test himself at a higher level. Danny Cowley would love him to stay but knows also that a fee for Curtis would significantly bolster the Fratton Park coffers. Expect him to go, even if the Blues play hardball with any offers that come in. They'll be wanting as much money as they can for one of their 'prized assets'.