Northern Ireland international McCullough has joined the Wirral outfit on loan until January 2, providing Rovers with room for manoeuvre to bring in another player in the middle of the park on a temporary basis ahead of the deadline on August 31.
McCann said: “The Ali Crawford injury has left us a bit short in the midfield area, definitely.
“Issam Ben Khemis has started to come to the party now. He is looking good. He has been a bit frustrated during pre-season in terms of match time and picking up a head injury in training and fighting his way back to fitness.
“Over the past week or so he has looked sharp. He is knocking down the door to be involved.
“But I still believe we need something in there that is going to be a little bit different to what we have.”
McCann is demanding an immediate response from Rovers after their 100 per cent record was ended in disappointing fashion with a limp 1-0 weekend reverse at Burton.
McCann, whose side start a three-match run of games at home in league and cup tonight, added: “We are looking for a reaction after the disappointment at the weekend. We have watched it back and learned from it, and we are ready to put things right.
“We have set high standards and have ironed things out and are all on the same page.
“Things have been sorted in training and the cohesion that might have been missing before will be there.
Last six games: Doncaster DLWWWL Shrewsbury WLLLLD.
Referee: D Drysdale (Lincolnshire).
Last time: Doncaster 1 Shrewsbury 2; September 26, 2017; League One.