Pompey fear Conor Wilkinson could miss another five matches as he remains sidelined through injury.
The striker has yet to train with the Blues since joining on an emergency loan from Bolton Wanderers more than three weeks ago.
Following agreement of the switch, his arrival was delayed through international duty with the Republic of Ireland under-21s.
Yet Wilkinson lasted only 39 minutes of their 3-1 Euro 2017 qualification defeat in Slovenia before he was forced off with a groin problem.
Since then he has remained at Bolton undergoing treatment.
The 21-year-old forward has already been ruled out of Blues fixtures against Carlisle and Dagenham & Redbridge.
It is anticipated it could be another two weeks before he even links up with his Pompey team-mates for the first time.
That would potentially be an absence taking in this weekend’s visit of Plymouth Argyle followed by York City, Wycombe, AFC Wimbledon and Hartlepool.
Although, Wilkinson could be available for the final match of the season against Northampton – in addition to possible play-off involvement.
The youngster was recruited by Paul Cook to bolster a strikeforce which will lose Michael Smith following the trip to Hartlepool on April 30.
The Swindon striker’s 93-day loan spell expires at that point, reducing Cook’s attacking options.
However, at that stage Wilkinson could be ready to come into the reckoning and provide the height to the Blues’ forward line in Smith’s absence.
Smith has scored twice in 12 matches since arriving on February 1. He has started the last four games.