The winger has been dogged by Achilles tendon problems, restricting him to only two appearances this season.
As a consequence, he has been a lengthy presence on a casualty list which has grown considerably during the festive period.
Lalkovic’s previous comeback from the injury was aborted in November following a Checkatrade Trophy outing at Charlton.
He presently isn’t even running outside as rehabilitation continues.
And Joe Gallen admitted the Blues have no timeframe for the former Chelsea player’s return.
Pompey’s assistant boss said: ‘Milan has been very unfortunate with his Achilles tendons – both of them.
‘If you’ve ever had an Achilles tendon injury, they are nightmares to get rid of.
‘They are six to eight-week injuries – and Milan’s had one on one side and one the other. Even when they are supposed to be okay they can come back, they are horrible injuries to have.
‘I’ve had it both sides as well and they just don’t go. They are horrible and linger and linger and linger.
‘There is no date on Milan coming back just yet and we want him back in as soon as possible, really.
‘There is no date I can give you. He’s not outside running, he’s not close. They are awful injuries to really get rid of 100 per cent.
‘They are horrible – and painful as well.’
Lalkovic has featured in just three Pompey squads this season, making two appearances, the other a league start against Walsall.
Signed by Paul Cook from the Saddlers in June 2016, the 25-year-old is out of contract this summer.