Guy Whittingham insists Josh Thompson still has a Pompey future.
The 21-year-old has joined League One rivals Colchester on loan until January.
In the meantime, his month-to-month contract will continue to be renewed, ensuring the Blues remain his parent club.
Thompson has played just three matches since cancelling his Celtic contract by mutual consent to make the move to Fratton Park in September.
He has been a constant on the substitutes’ bench, prompting former manager Michael Appleton to put him up for loan in a bid to get him games.
Now the defender is at Colchester, where he was an unused substitute in their match with Crewe last weekend.
But Whittingham doesn’t believe it will necessarily be a permanent switch.
Pompey’s caretaker manager said: ‘Josh was one of those who needed some football, he needed to go out there and play.
‘Of course, with him gone we are now looking to replace him.
‘He can come back, it’s not like he has gone forever. He could come back in January, absolutely.
‘It’s just that he’s a young kid, only 21, and I don’t think he has got the mentality of League One.
‘Maybe in two or three years time he may be experienced, but we’ve got a squad of 20 and can’t afford to have that inexperience at the moment. We have got to have ready-made players.
‘We haven’t got time to bring him through. He’s maybe another year on from being a development group player.
‘He has been up in Scotland with Celtic miles away from the league football we are playing down here.
‘We are looking to bring in someone who has got a bit of an idea of the game at this level, who is big and strong and can win some headers.’
Thompson’s most recent Blues appearance came in the 2-1 home defeat to Walsall in mid-September.
He missed two weeks earlier in the season with an ankle injury.