McLeish recalled Darlow from a loan spell at Walsall and put him straight into the starting line-up for the npower Championship game at home to Peterborough on Saturday.
The 22-year-old played well as Forest triumphed 2-1 but he seems destined for a spell on the bench when McLeish signs another keeper.
"Karl was marvellous," said McLeish after the game. "The kid was really cool. I just told him to do what he had been doing to get into the team. I told him he did not need to be fancy or add anything to his game.
"The reason he was playing was because of what we had already seen in him. He handled it really well, great credit to him for that.
"He made a good save at an important time for us. He had a very good debut for us. He is 22 now and that was the reason for the Lee Camp decision. We felt that Karl could play. But we will still be looking for an experienced keeper.
"I don't know how long that is going to take. It is not easy to say it will be in 24 hours or that it will be within a week - it is an on-going process."
Meanwhile, McLeish was pleased with Gonzalo Jara Reyes' debut for the club after the Chilean right-back played the full 90 minutes against Posh following his arrival on loan from West Brom.
The Scot added: "Jara looked very competent on his debut, considering he has not played for a while.
"He has good fitness, he is quick and his use of the ball is good, having grown up in South America. Being a Chile international, he is comfortable in possession. He had a decent debut, to be fair to him."