19 year-old McManus penned a two year deal at the Alex after catching the eye of the Neil Baker in a recent match.
McManus came through the ranks of Manchester United but failed to make the grade at the Old Trafford club. After he left United the player drifited out of the game but recently featured in a 2-1 win over Nottingham Forest in a pre-season friendly.
After the friendly McManus was offered a trial at the Championship club and it was understood that Forest wanted to sign the youngster but with Crewe intervening McManus plumped for Crewe.
McManus told the Official Site "I'm hoping that by coming here I can follow in the footsteps of all the other great players who have come from this club. It has a good history for producing players.
"I've just been to Nottingham Forest on trial as well, but I've signed for where I preferred to come. I have a better opportunity here I think, there is a better chance for me to progress with my career."