The third longest-serving skipper in Scotland's history believes Fletcher showed his class in Milan last week when he reduced another English icon, David Beckham, to a bit-part player in one of the world's great footballing cathedrals.
McAllister told the News of the World: "England are claiming Wayne Rooney as the greatest player in the world after his two goals in the San Siro.
"But Darren Fletcher was right up there with him as United's most influential player on the night. Personally I think people use the term world class a bit loosely these days. That's why I always hesitate to give anyone that distinction.
"But there's no doubt Darren is well down the road to becoming a world class player. Let's put it this way, over the next couple of seasons he's going to have plenty of opportunity to show he really is in that class.
"Well there's every chance Manchester United and Barcelona's paths are likely to cross in the Champions League before long. Darren is also going to come up against Iniesta and Xavi twice when Scotland play Spain home and away in our European Championship qualifying group.
"If he comes out on top of those encounters then we really will be able to say Scotland has produced a world class player again."