The Scotland skipper admits he has fallen short of his own high expectations during the wretched Group Nine campaign.
Fletcher said: "I owe George a performance, I don't think I've had my best games for Scotland under the manager.
"I don't know why that has been. I feel I've not done myself justice in his teams.
"I've given 100 per cent and tried as much as I have in any other game but the performances haven't been there.
"I know that myself and I'm desperate to do well for him.
"I'm bitterly disappointed when that happens and it does affect me.
"I put more pressure on myself than anybody knows. Maybe sometimes you can try too hard to do well and it doesn't come off."
Fletcher has been a key player for United already this season but Scotland fans argue he never delivers on the international stage.
Fletcher, 25, who wins his 44th cap today, added: "It's hard playing a certain way week in and week out then, for one or two weeks, having to change your style completely.
"That's something you have to learn to do every week at international level.
"But I'm desperate to put in a performance for the manager and the country.
"I accept the responsibility which comes with being a captain. With United I know my role in the team - it's not the person who has to go and win the game.
"It's not the person who has to make the big pass or score the goals - I'm the player that gets us playing.
With Scotland, there is more pressure on me to go and play that killer pass or create goals." Fletcher agrees with James McFadden that it is the players and NOT the boss who are at fault for the team's World Cup woes.
Booze-ups, bust-ups and cock-ups have stalked Scotland, shredding the feelgood factor built up following the heroics of the Euro 2008 qualifying campaign.
Fletcher admitted: "A lot of players have let the boss down.
"That's in terms of our performances and things off the pitch.
"But he has not let that shine through and has always been there to lead by example.
"He is constantly encouraging and playing things down and always saying we've still got a great chance.
"All the lads have found a great respect for him in this campaign and are desperate to go out there and do it for him."