Instead he believes the right-back is destined to remain in the Championship next term.
Romeo has made 41 appearances for the Blues since arriving on a season-long loan in August.
However, he started just one of the Blues’ last seven fixtures, with Hayden Carter preferred for the League One finale, and is again expected to be on the bench at Sheffield Wednesday on Saturday (12.30pm).
By Cowley’s own admission, the 26-year-old couldn’t maintain his impressive form from the first half of Pompey’s campaign.
And with Cardiff previously linked with a player who has made it clear he possesses no future at Millwall, that could well be his next club.
Cowley told The News: ‘I don’t think it would be possible for us to keep Mahlon from a financial perspective.
‘I would anticipate he'd stay in the Championship.
‘Mahlon had a brilliant start to the season, giving us real athleticism, pace, power and robustness.
‘You only have to look at how few goals we’ve conceded down the right-hand side of the pitch to know he did a really, really good job for us.
‘He probably hasn’t quite found the same level of consistency in the second half of the season.
‘Sometimes, for whatever reason, they are not quite able to find the same level, maybe off the back of the Covid period.
‘Hayden Carter has come in and probably performed beyond all of our expectations. As a consequence, Mahlon hasn’t been able to find as much recent game time as he would have liked.’
Certainly Romeo failed to retain the heights he set himself during the opening four months of his Fratton Park stay.
Form noticeably dipped at the turn of the year, yet he remained a first-team regular and solid performer.
Overall, he proved a good loan addition, particularly in defensive situations, and will be a fine addition wherever he next finds himself.
Cowley added: ‘He’s a very good one-v-one defender and has unbelievable athleticism and power.
‘You add to that Mahlon’s change of direction and he’s very, very difficult to beat, while very good at stopping crosses.
‘We have conceded very few goals from that side of the pitch.’
A message from the Editor, Mark Waldron
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