Bishop's wife went into labour on Thursday, meaning the midfielder may opt to remain in Nottingham.
With County out of the FA Cup, Keith Curle's side have not played since New Year's Day - and the manager has seen his squad change drastically since.
Striker Chris Iwelumo has returned to Watford after his loan spell ended.
Defenders Carl Regan and Tom Williams have been allowed to leave the club while veteran striker Lee Hughes has also departed, signing for npower League Two promotion chasers Port Vale.
However, Andre Boucaud will be available on the south coast after the midfielder returned to Meadow Lane on a permanent deal from Luton this week.
Midfielder Jordan Stewart and defender Damion Stewart are both in negotiations over new deals after their short-term contracts ended at the turn of the year. The latter would miss out at Fratton Park anyway through suspension.
Meanwhile, Curle is trying to sign Craig Beattie as Hughes' replacement but faces a race against time to get him in the squad for Saturday.
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