McCoist had said the Ibrox club would be happy to play any team – including the Scottish champions – in the last eight.
However, SportTimes columnist Johnstone believes Rangers had no chance of beating their city rivals with so many players out injured.
Big Derek said: "The last thing Rangers would have wanted was Celtic. If we are being perfectly honest, they can compete with any other side in the SPL on their day at the moment. But Celtic would have been too much for them with the experience and the good players they have got.
"I am sure Rangers fans would have been dreading getting Celtic while Hoops supporters would have desperate to get Rangers.
"I think Ally will be delighted to get a home draw and delighted to avoid Celtic."
Johnstone, though, thinks Rangers will have a slim chance of beating Celtic if they overcome Inverness Caledonian Thistle in their quarter-final at Ibrox at the end of the month.
McCoist is without forward Andy Little, winger David Templeton and striker Francisco Sandaza at the moment due to a injuries.
He is hoping to have Ian Black and Dean Shiels, who both missed the William Hill Scottish Cup showdown with Forres last weekend, back for the Saturday's game against Stirling Albion at Forthbank. Johnstone added: "If Rangers get through this game there is a one-in-three chance they will get Celtic in the semis.
"They would be better placed to beat them then. They could have all their players back by that stage and would have a chance.
"But at this stage, no. Just look at the Celtic side. They have the best squad of players in Scotland by a distance. In fact, their second team would probably be good enough to win the SPL this season.
"Beating Inverness will not be easy, but Rangers showed they can get themselves up for a game with an SPL team in the last round and they can do so again."