Morgan went off at half-time of last weekend's derby win over Sheffield United with an ankle injury while O'Connor has returned from international duty with Northern Ireland with a groin strain.
Kari Arnason (Iceland) has returned unscathed from his international exploits and Mark Bradley (groin) has recovered from the injury which kept him out against the Blades.
Striker Daniel Nardiello has shaken off a slight hamstring strain, but David Worrall (groin) is unlikely to be fit.
Oldham could be without key defender James Tarkowski when they travel to the New York Stadium.
The 20-year-old earned rave reviews after a sterling performance against Preston on Monday night but received a knock to the leg in that defeat and is rated as doubtful.
Latvian midfielder Edijs Joksts injured his knee in a reserves game in midweek, although it was doubtful he would be involved anyway.
Midfielder Albert Rusnak is available again after international duty with Slovakia Under-21s but full-back Connor Brown will definitely be out with a knee injury, however he will not miss the rest of the season as first feared.
Source: PA