The goalkeeper broke three bones in his hand after colliding with Blackburn Rovers striker Shabani Nonda in the final game of last term.
He has been forced to sit out the USA's Gold Cup-winning campaign and also the Copa America in Venezuela.
But Hahnemann is back in light training with Reading and expects to be between the posts for the 11th August visit to the Premier League champions.
"I'll definitely be at Old Trafford," Hahnemann told the club's official website.
"I had a check-up two days ago in Colorado and the doctor was really pleased with everything.
"He said I was fine for some light training and then in two weeks I'll have more X-rays and we'll take it from there.
"What we don't want is for me to take a shot and to have the hand bent backwards. We're just building up nice and slow, and going by pain as a guideline.
"There were no problems in training yesterday. I did some light stuff, some throwing, a bit of footwork."
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