Grayson was sacked after the Black Cats drew 3-3 at home to Bolton, marking the 19th home game without a win.
And you've been telling us what you think on social media.
Who should SAFC appoint next? When did it all go so wrong for the club? What would you like to see happen?
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Here are some of your thoughts from Facebook.
Jass Smith: "No he wasn't the perfect candidate. It isn't a nice thing, no. Yes his sacking is deserved. Gary Monk's assessment gets one out of three from me."
Angela Tasker: "Club never been as good since Reid left but a 2nd time? Oooo I don't know if that's the right road to go down. I'd sack all the team and start from scratch."
Margaret Bunbury: "And another manager goes! Is it not the player's that need sacking!"
Diane Kay: "Can't blame the managers 100 % as they can only do what ever they can with the money they have."
Linda Grierson: "Just watched the conceded goals, oh dear me, hat the heck does the keeper think his job is?
No effort at all to make a save, second goal he stood in front of the loose ball, allowed an opposition player to take it without challenge and then retreated to his goal to watch the opposition fire into the net ... no attempt whatsoever to save.
"Big streak of rubbish, defence just as appalling."
Michael Watson: "Gonna make our situation no better, no manager now, games coming up, and logically we are in this position for the same reason.
"Bringing a manager in quickly and having no funds, or transfer window and having the same players ?
"We're back to the same position we were in wen the last one went ...the clubs gonna end up bringing some face in out the blue and no doubt it wont be anyone known."
Eric Redfearn: "A tragedy for Sunderland who are in a terrible mess. Very unfair to Simon Grayson who inherited a poor squad with little money to replace players.
"I wish him well, but Sunderland have a terrible battle on their hands and look destined for another relegation."
Jack Burton: "Liked him as a person like. Good man just not good enough for the job. Doesn’t help when you’ve got deluded fans like either."
Mackem Mick Robins: "Player power wins every time. Players should be paid on their performance and [work rate].
"Don't put shift in don't get paid. Think wor Kev should get a chance. To stop us being a laughing stock. Come one you reds. Show some pride when you step out on the pitch."
Linda Hendry: "Laughing stock that's what we are and it breaks my heart to say it."
Darren Grainger: "He was a nice bloke who said positive things which was a welcome change after Moyes’ negativity. We were too hard a task for him and you could really see that in the last few games."
Shaun Sayers: "It's unfortunate but it is far from mind boggling and, given the situation was deteriorating despite players coming back from injury, it's hard to argue that it is undeserved."
Nick Safc: "The problem is the owner, not the manager."
David West: "It doesn't matter how exciting the name is, absolutely nothing will change until we have a new owner. Nobody in their right mind would touch the club at present."
Doug Roper: "Much as I love Reidy and the great team he built, he’s not the solution. He’s no longer actively managing in the game.
"I’m not going to pretend to know who the best manager for us would be right now, but I’m pretty sure going back to Reidy isn’t the answer."
Stephen Virtue: "Whatever the rights and wrongs of this ridiculous situation the fact is that squad of players should be better than 3rd bottom of the league."
James Potts: "Really disappointed, I wanted the guy to succeed and for the club to move away from this constant manager change. But it looks he was clearly out of his depth!"
Ken Hughes: "What a joke this club has become."
Dave Mitcheson: "Pleased he’s gone but terrified as to who’ll be next. Must be Halloween."
Michael Gallagher: "He was way way way out of his depth. He talked a good talk but ONE win all season spelled his fate. Who will want the job now though?"