Pompey had hoped to still be in the race for automatic promotion ahead of Saturday’s tea-time clash with Accrington (5.30pm).
But a midweek defeat to Peterborough means they now cannot catch Luton and Barnsley at the top of the League One standings.
It means the Blues will compete in the play-offs, although they do not yet know who they will be playing.
If Kenny Jackett’s side remain in third spot, it would be a trip to either Doncaster or Peterborough next weekend.
Dropping down to fourth or fifth position, however, would mean they take on Sunderland or Charlton. Click here to see a list of dates.
Pompey will reach the 90-point mark if they can secure victory over Accrington, a feat they have not managed since winning promotion to the Premier League in 2002/03.
Their opponents secured their place in the third tier for another season with a 5-1 rout of Plymouth last week.
It leaves them sitting 13th in the table, although they are unable to catch Oxford and end up in the top half.
Oli Hawkins’ goal was cancelled out by Michael Ihiekwe when the sides met at the Crown Ground back in October, with Craig MacGillivray having earlier saved a penalty.
Pompey are close to having a fully-fit squad to choose from, with Jack Whatmough (knee) the only player missing.
Callum Johnson (ankle) is doubt for the visitors, but goalkeeper Dimitar Evtimov is available again following a two-match ban.
HEAD TO HEAD
Pompey: 6 wins
Accrington: 2 wins
At Fratton Park
Pompey: 4 wins
Accrington: 1 win
Fratton Park is full to capacity for this fixture and no more tickets will be made available.
Supporters are advised to get to their seats early, as from 5pm, a host of Player of the Season awards will be presented.
A minute’s applause will also be held before kick-off in memory of all those Pompey fans who have passed away over the course of the campaign.
The players will return to the pitch after the final whistle to take part in a lap of appreciation.
Due to railway engineering works over the bank holiday weekend, a replacement bus service will run between Fratton and Havant/Petersfield/Chichester. Click here for more details.
Overseas subscribers and match pass holders can watch the action – now with on-screen graphics – and commentary will begin from around 10 minutes before kick-off.
ALSO IN LEAGUE ONE
Blackpool v Gillingham
Bradford v AFC Wimbledon
Bristol Rovers v Barnsley
Charlton v Rochdale
Doncaster v Coventry
Luton v Oxford
Peterborough v Burton
Plymouth v Scunthorpe
Shrewsbury v Walsall
Southend v Sunderland
Wycombe v Fleetwood