Michael Appleton has revealed Chris Maguire had been set to make a Pompey loan return.
But the switch was scrapped on Sunday after the striker damaged medial knee ligaments while training for Sheffield Wednesday.
Last season Maguire was a highly-popular figure at Fratton Park with three goals in 11 matches.
This summer he was transferred from Derby to the Owls, only to feature just once in the Championship for his new club.
That prompted Dave Jones to agree to an initial one-month loan deal – only for injury to intervene.
As a result, Appleton recruited Scott Allan at the 11th hour to replace Wes Thomas.
But the loss of Maguire comes as a major blow.
He said: ‘We had everything lined up with Sheffield Wednesday.
‘They were more than happy for him to come.
‘He was training there Sunday morning and was due to meet us at the hotel on Sunday night.
‘Then he turned quite sharply in one of the sessions and has done his medial ligament.
‘I am not sure how bad it is but when I spoke to him on the phone yesterday afternoon after a scan, they think it is going to be around the six-week mark.
‘That pretty much sums up the luck we are having at the minute.
‘Chris has not played a lot of football at Wednesday and we have been trying to do this for a while but they have not wanted to do it.
‘We kept asking, kept pestering and they were happy to do it as long as the lad was.
‘I spoke to him and he was desperate for it to happen.’