McGregor's amazing recovery from a groin injury has handed boss Craig Levein a major boost ahead of tomorrow's vital first qualifier on against Serbia at Hampden and the midweek clash against Macedonia.
And last night, two Scots goalkeeping legends said the former Rangers talisman may be the key to Scotland ending a 16-year absence from the biggest event on planet football.
McGregor missed last month's friendly against Australia last month, but played for new Turkish club Besiktas on Saturday and kept a clean sheet in a 3-0 win over Kardemir.
And Ibrox legend Peter McCloy said McGregor's experience would be critical. He said: "He is a big game player and they don't come much bigger than the opening game of a World Cup qualification campaign.
"He has played in many big games for Scotland and always delivered for us. The fact he played a game in Turkey at the weekend will have given the squad a huge boost.
"Allan knows his defence and they know him and there is an excellent understanding there and that is an absolute must for any international side."
And McGregor was also given a huge vote of confidence from former Scots World Cup keeper Alan Rough.
"I think it's all about the goalkeeper," said Roughie.
"Goalkeepers win games and people forget that. if you don't have a top goalkeeper, the goalkeeper who can win you a game, then you're not going to get anywhere.
"In the Champions League last year, Petr Cech won the Champions League for Chelsea. The quality of a keeper like Allan can win a game for us.
"Serbia are going to have something, he's going to have to make a save. When that shot comes in, you've got to be mentally prepared. Allan, over the years, has proved he can do that."