Hermann Hreidarsson told Pompey's owners: Don't sell David Nugent.
The fans' favourite has warned the Blues they can't afford to cash in on the striker in January.
Nugent has been flying of late, grabbing six goals in his last 12 outings.
That has sparked speculation about his future, with the likes of Blackpool and Wigan said to be interested.
The 25-year-old has said he is happy to remain at Fratton Park, though.
And Hreidarsson has made it clear Pompey can ill afford to lose their main source of goals.
He said: 'David is going nowhere – I won't let him. He and Dave Kitson are two strikers who have done well for us.
'Nuge was outstanding at Norwich recently. He showed his class and pace.
'It was the same against Millwall. He's probably one of the quickest in the league.
'He's scoring goals as well and we need them.
'Strikers are there for that and that's why they are often the most important players.
'He's important for us.
'We need all our players. We can't afford to let anyone go. Everyone has an important role here.'
Pompey's new regime are being hindered by more inherited off-the-field issues over contracts at present.
That's is giving Steve Cotterill an additional headache, but Hreidarsson said the players can't let the squad issues bother them.
He said: 'Eventually you get used to it.
'Things like that have been around for long enough now.
'You try to focus on your own game or what you can do for the team.
'You look at only the things that you can affect, really.
'There's is nothing we can do about them as players.'