And Pompey’s head coach is ‘99.9 per cent sure’ the club option will take up their contract option on the leading scorer.
The winger is basking in a rich vein of goal-scoring form, registering seven goals in his last 11 outings, taking his season’s tally to eight.
Certainly Cowley is braced for approaches for a 25-year-old whose deal expires next summer.
Crucially, however, the Blues possess a club option on Harness, who they recruited from Burton in July 2019 for a fee of around £800,000.
Cowley told The News: ‘We are a football club that’s trying to get better. If we lose our best players that becomes really difficult.
‘There is no pressure at all from the owners to sell any of our best players – and they have said that from the moment we came in. They’ve been incredibly supportive in that way.
‘Unless you are Manchester City, Chelsea, PSG, I wouldn’t use Barcelona now as an example, maybe Real Madrid, maybe not, but you are pretty much a selling club.
‘If the right club comes in for one of your players, then sometimes you have to make the right decision for the long-term future of the football club.
‘However, it’s absolutely our ambition to keep our best players here.
‘I would think there will be interest in Marcus in January, unless the football world is blind, which I don’t think it is.
‘He’s a top player, a top, top player. Only Marcus controls his destiny, he can be whatever he wants to be.
‘The summer was really quiet, that’s the honest truth, and there were low-level phone calls (about him), but nothing that went beyond that.
‘He obviously has an option on that contract and I am 99.9 per cent sure that, at some stage, the option is going to be taken up.
‘I don’t think there’s much of a story there.’
Harness, who attracted interest from Blackburn during the summer, has now netted 27 times in 108 Pompey outings.
Cowley added: ‘Marcus and his representatives will know that, at some point, we are going to have to take that option.
‘I don’t think it’s fair for me to speak about the personal details of a player's contract, but it’s on our terms and we are in a good position with it.
‘We obviously paid significant money for Marcus and, as a consequence, the contract reflects that.
‘In general, there are different types of options. Club options, player options, options related to performances, the number of appearances and divisions you are in. Sometimes the wages stay the same, sometimes the wages go significantly up.
‘These are variables you have to be aware of.’
A message from the Editor, Mark Waldron
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