Paul Cook said Pompey were doing their best to bring in reinforcements before the end of the January transfer window.
The Blues are keen to sign Preston North End striker Eoin Doyle on loan until the end of the season.
But any potential move is proving complicated, with Bolton also heavily linked with the Irishman.
Preston, meanwhile, are keen to add to their own striking ranks before letting the former Chesterfield marksman leave.
Cook is determined to bolster his attacking options, with Pompey currently sitting outside League Two’s automatic promotion places.
And he stressed it was a case of wait and see whether any pursuit would prove successful.
‘I think our fans have to trust people who run the club,’ said Cook during his press conference ahead of Saturday’s visit of Exeter.
‘As a Pompey fan, you’ll be looking at us and wondering, will we be active before the market ends?
‘But we are doing our best. If we are not and we don’t bring someone in it won’t be for the want of trying.
‘And the club are backing me 100 per cent in that pursuit.
‘We just have to watch this space.
‘We can’t guaranntee anyone coming in.’