Shrewsbury's plans for this weekend's visit to the Northern Commercials Stadium have been disturbed by the exit of Mellon and assistant Mike Jackson on Thursday afternoon.
Shrews goalkeeping coach Danny Coyne is scheduled to take charge against McCall's men, as City aim for their third league win on the trot.
McCall is wary of a reaction from Shrewsbury's players on Saturday with a new man in charge, citing Coventry's recent victory at Port Vale following Tony Mowbray's departure as a reason for caution, but he knows City can only concentrate on their own game.
Speaking about Mellon's exit from Shrewsbury, McCall said: "I don't think it will make our job any easier that is for sure.
"You only have to look at Coventry City recently.
"Tony Mowbray left his job, the assistant came in, they went to Port Vale, a side who had won all five of their home games up to that point, and they picked up their first league victory of the season.
"I'm sure the Shrewsbury players will be trying to impress any potential new managers who might be watching - we expect our task to be a little bit more difficult now if anything.
"Having said that, we'd noticed in their last two games that they have changed formation so we haven't done too much specific shape work on them.
"We naturally do our homework on the opposition but we wanted to keep ourselves open to one or two different things.
"Also, with us being at home, we have to focus mainly on ourselves.
"We can't worry about Shrewsbury, we can only think about us and making sure we are ready to start the game on the front foot.
"There will certainly be no complacency from our point of view."