The Pompey boss has denied holding an interest in the 22-year-old as he bids to find a replacement for Marcus Harness.
Last week Diamond’s name cropped up in reports as Cowley weighs up his options for the vacant right-wing role.
The Blues are hoping to add to their ranks in that position before Saturday’s visit of Lincoln to Fratton Park, with Ronan Curtis and substitute Reeco Hackett featuring there during the season-opener against Sheffield Wednesday at the weekend.
Predicted Portsmouth XI v Cheltenham: changes expected to side that beat Cardiff so handsomely - but attacking duo could keep places and defender set to return
Portsmouth transfer news: Blues youngsters attracting interest but Danny Cowley has no desire to cash in just yet
Portsmouth boss Danny Cowley makes transfer admission as former Luton and Millwall midfielder edges closer to Fratton Park exit
Former Portsmouth keeper Alex Bass suffers tough night on and off the pitch as he makes Sunderland debut following Fratton Park exit
League One latest: Oxford land former Pompey striker target from Swansea as Sheffield Wednesday bemoan exciting duo's move to Brentford and former Peterborough boss criticises club
But, according to Cowley, the Black Cats youngster is not someone he is actively tracking, despite Diamond making an impression during his loan spell at Harrogate last term.
Indeed, the Sunderland academy product scored the winner for the League Two side when they dumped Pompey out of the FA Cup.
When asked about the forward by BBC Radio Solent, Cowley admitted he was not looking to make Diamond his 10th new addition of the transfer window.
He said: ‘Jack’s a player we know well.
‘He ruined our FA Cup involvement last year with a very good performance against us.
‘He’s obviously a Sunderland boy who’s come through the academy there.
‘He’s a good player, but for us, no, we have clarity about what we would like to bring in and we’re working hard to achieve that.’
Diamond was not involved in Sunderland’s Championship opener against Coventry on Sunday.
Last season he scored 13 goals and recorded six assists for Harrogate in League Two.