Preston are set to be without captain John Welsh as they welcome the O's
The midfielder was withdrawn during the first half of last weekend's 1-0 defeat at Brentford with an ankle injury and is unlikely to recover in time for the clash.
John Mousinho was Welsh's replacement at Griffin Park and is the favourite to start in central midfield while Keith Keane is another alternative.
Bailey Wright (ankle) and Will Hayhurst (hamstring) were both ruled out against the Bees and will face late fitness tests ahead of the game.
Joel Byrom (hernia) and Scott Laird (broken leg) are also on the road to recovery but the match against Russell Slade's men will come too soon for both.
Manager Simon Grayson has so far resisted the temptation to enter the loan market to bolster his squad and is keen to keep faith with his current group of players as they look for a positive end to the campaign.
Leyton Orient are hopeful Dean Cox will be fit for the trip to Deepdale.
The winger sustained a shoulder injury during last weekend's 4-1 win over Carlisle, in which he scored the fourth goal, but is expected to be available.
Mathieu Baudry will miss out again with a hip problem and is not expected back until after Easter but fellow defender Nathan Clarke came through against Carlisle unscathed after shaking off a rib injury.
Boss Russell Slade has four strikers to choose from for a change as Kevin Lisbie, Shaun Batt (both hamstring) and David Mooney (thigh) are fit after recent lay-offs.
Lisbie started alongside Batt against Carlisle with Mooney and Charlie MacDonald replacing them during the second half.