But chief executive Andy Cullen believes their prized ‘asset’ will inevitably attract strong interest from suitors.
Cullen admits that puts the Blues in a good position to avoid losing the seven-goal winger should clubs come sniffing.
Blackburn were among admirers in the last transfer window, although Pompey’s chief executive insists no bids were received from any club.
Nonetheless, he is adamant they want the talented Harness to remain at Fratton Park beyond next summer.
Cullen told The News: ‘We would like to keep Marcus, 100 per cent, he is a big part of Portsmouth Football Club. He’s a quality player and he can play at a really, really good level.
‘He’s an asset, although it’s a situation where you are not in full control with somebody (another club) coming in. Who knows what might happen with Marcus going forward, but we’ve got some protection.
‘Marcus has always attracted interest, but the club have never had a firm bid from anybody, so it's not one we turned down at all in the last transfer window. But we know clubs were enquiring.
‘All our players are assets and Marcus is an asset we do have some protection over at the current time.
‘But what we are not in control of is interest from other clubs.
‘He’s had a fantastic season, so let’s look at the positives. He is one of the stand-out performers this campaign in terms of the goals he’s scored.
‘I can see the potential that exists for Marcus going forward – although I don’t want to talk him up too much!’
Harness has netted 26 times in 107 appearances since arriving from Burton in July 2019.
He has been a key performer during the last two-and-half seasons, primarily on the right wing.
Cullen added: ‘It’s for the manager to determine the players he wants to do with the players – and a question you should put to Danny.
‘In terms of his squad, what he wants to build, what he wants to mold, should Danny see it as really, really important that we keep Marcus, then of course, as always, we will back the manager.’
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