McCall has already secured five new players into his squad ahead of the club's season opener with Port Vale on 6 August but he believes further editions are still required.
The City boss is keen to push on with the recruitment drive but he is aware that the club might have to be patient in their pursuit of some targets.
He said: "We have made enquiries about a few players and there is the loan market to look at as well.
"The loan options might have to wait until into the start of the season or even the last few days of August before the (transfer) deadline though.
"Managers might look to keep their squads as strong as possible for as long as possible until they know exactly what shape they will be in for the new season.
"Some players might also be holding out for options in the Championship before looking to League One level.
"We're doing a lot of hard work behind the scenes trying to set things up but we're in the same boat as a lot of other clubs.
"Other managers I have spoken to also want those extra numbers in but is all about getting the right sort of player in.
"We know the areas of the pitch we need to strengthen and we are trying sort it out in the best way we can."