Pompey, meanwhile, have made a solid start to the campaign after drawing their opening league game and winning Tuesday's EFL Cup tie.
Match preview
After earning promotion from the fourth tier last season, Leyton Orient are participating in League One for the first time since the 2014-15 campaign.
Their long-awaited return to the third tier of English football began with a narrow 1-0 defeat to Charlton Athletic at The Valley.
They were unable to bounce back in Tuesday's EFL Cup tie against Plymouth Argyle, losing 2-0 following a first-half brace from Ben Waine.
After being eliminated in the first round for the third consecutive season, the O's will now focus on their first home game of the season.
Richie Wellens's side ended the 2022-23 campaign with the second-best home record in League Two, and they will be hoping to reproduce that form in the third tier.
In contrast to their hosts, Portsmouth have made an unbeaten start to the new season, which began with a 1-1 draw against Bristol Rovers last weekend.
They looked to be heading towards defeat after Luke Thomas opened the scoring for the Gas, but Pompey managed to snatch a point thanks to Kusini Yengi's stoppage-time equaliser.
After coming off the bench to mark his debut with a goal, Yengi made another positive impression in Tuesday's EFL Cup tie against Forest Green Rovers.
Yengi's brace and a Zach Swanson effort helped Portsmouth come from behind to claim a 3-1 away win and seal their place in the second round.
John Mousinho's side will now turn their attention back to League One action, and they will be looking to extend their 12-game unbeaten league run (W4, D8), having avoided defeat since losing 1-0 to Sheffield Wednesday in March.
Leyton Orient League One form:
L
Leyton Orient form (all competitions):
L
L
Portsmouth League One form:
D
Portsmouth form (all competitions):
D
W
Advert - content below:
Team News
After making a number of changes to his Leyton Orient side for the midweek cup tie, Wellens could revert back to the lineup that started against Charlton last weekend.
Solomon Brynn will start in goal for the hosts, and he will be shielded by the back three of Omar Beckles, Daniel Happe and Tom James.
Joe Pigott, who spent last season on loan at Portsmouth, will be looking to open his account for the campaign when he faces his former side on Saturday.
As for Portsmouth, they are expected to be without the services of Tom Lowery, who was forced off at half time last weekend.
Northern Ireland international Paddy Lane is also unlikely to feature after missing Pompey's opening two games with an injury issue.
Despite scoring three goals in his first two appearances for the club, Yengi may have to settle for a place on the bench, with Mousinho expected to keep faith with Colby Bishop as his main centre-forward.
Leyton Orient possible starting lineup:
Brynn; Beckles, Happe, James; Hunt, Pratley, El Mizouni, Sweeney; Sotiriou; Archibald, Pigott
Portsmouth possible starting lineup:
Norris; Rafferty, Poole, Towler, Ogilvie; Morrell, Pack, Saydee; Whyte, Scully, Bishop