Carter was forced out of the reckoning earlier this week when the shoulder injury he picked up in the dying stages at Westpac Stadium failed to respond to treatment.
All Blacks coach Graham Henry raised a few eyebrows when he handed MacDonald the number 10 shirt as the home side attempt to secure only the third 'black-wash' in Lions history. The other two were in 1966 and 1983.
But his plans were thrown into disarray when a niggling groin injury forced the Canterbury man to pull out.
Chiefs backrower Sione Lauaki is also a late addition to the starting XV after openside flanker Richie McCaw had to withdraw due to a hamstring pull. Rodney So'oialo will move into McCaw's position with Waikato's Marty Holah added to the bench.
Henry has no qualms in giving the rookie 21-year-old McAlister his international debut, even though he brought Otago's Nic Evans into the squad as cover for MacDonald. With McAlister jumping the queue, Evans has been deposited on to the replacements bench.
"Luke will navigate the ship as best he can," said Henry. "He's going to have a lot of support.
"He's got Tana Umaga there alongside and Byron Kelleher inside.
"The game plan is pretty simple anyway, and we certainly don't have to simplify it any further. I think Luke will do okay, obviously. There are still a couple of days to work on combinations."
McAlister has played most of his recent rugby at inside centre - he played for the New Zealand Maori against the Lions in there - and concedes he has not "a hell of a lot" of experience in the crucial fly-half role but he remains unfazed with the challenge ahead.
"It's just one step closer in, that's all," he said.
"I'm sure the boys will look after me. There is a lot of experience in the All Blacks and I've been with them all week. So it's not as if I don't know them at all."