That’s after the Blues received a bid for an unnamed member of Danny Cowley’s set-up very late in the window.
The offer was ‘way blow’ the valuation the club have on the player.
But it was significant enough interest to prompt Cowley and his recruitment team to identify possible replacements.
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No deal was struck for either player, with the former staying at the Millers and the latter ending up at Wycombe.
Indeed, the Blues’ only new arrival when the clock was ticking towards Monday night’s 11pm deadline was a short-term move for Sunderland forward Aiden O’Brien.
Nevertheless, all that could have changed if a more acceptable had been offered for the unnamed player.
Providing a January update via Pompey website, Cullen said: ‘The other thing we were sort of looking at at the end of the window was we did have some interest in one of our players very, very late in the day.
‘The valuation was way below what we would expect and we made that quite clear.
‘But there was always a risk that somebody might come back with a price that we were interested in.
‘So we then started to look at potential replacements just in case that happened.
‘But, the same as us, we got to a situation with that particular player where his club didn't want to release him, either, unless there was a significant transfer fee being paid which will not be that price probably later on when we get to the summer.
‘So, that was a little bit of excitement right at the end, but our player stayed with us, which is good news and, again, we didn't have to process that alternative option.’