Grant, 39, joined United three years ago from Stoke for £1.5million to occupy a back-up role at the club, where he made two competitive appearances in four seasons.
The veteran shot-stopper enjoyed an impressive career which saw him make over 500 appearances, mainly in the Championship, before spending the final six years in the Premier League with Stoke and United.
He never managed to get regular playing time for United and was even listed as a coach on some team sheets last season, but still signed a one-year contract extension last summer.
“After 511 appearances, I’ve decided it’s the right time to move into the next stage of my career,” he told club media.
“There have been so many fun moments mixed in with the odd challenge, but I’m grateful for each and every one.
“Fulfilling a boyhood dream of playing for Manchester United was something I thought was out of reach, so to have achieved that fills me with great pride and emotion!
“Although I haven’t played as many games in the last four years, I’ve given everything to the group every single day on the training pitch and in the dressing room. The opportunity to join the biggest club in the world was one I could never turn down and I’m so grateful for the lessons learned and the friends I’ve gained.
“The opportunity to challenge, set standards and ultimately learn from some truly exceptional players and staff has been so valuable.
“I’ve been extremely fortunate to play for some amazing clubs, Derby County, Oldham Athletic, Sheffield Wednesday, Burnley, Stoke City and now to finish at the pinnacle – Manchester United. I’m thankful to each and every club for what they have given to me, each one has shaped me into who I am. The relationship with the supporters of these great clubs will always be one of my most treasured memories.
“There are too many incredible football people to thank as I’ve received untold amounts of help from so many special people over the last 23 years. I do however want to say a huge thank you to my family and in particular my wife, Helen, for moving around the country with me, allowing me to pursue my dream. Football has given me so much, but it can also be tough on partners and children. Without them it would never have been possible to achieve what I did.
“As I move into the next stage of my career, I’m excited and hu…