Simon Grayson pulled no punches in his post-match assessment at the Stadium of Light, admitting the result must come as a wake up call.
The Black Cats pre-season ended in disappointing fashion, as Brendan Rodgers’ treble winning Celtic romped to a 5-0 victory to lift the Dafabet Cup.
It was a frustrating afternoon for the men in red and white, however, it might have been so different had James Vaughan found the back of the net after an early Callum McGregor double.
Jonny Hayes added a third before half-time and then McGregor completed his hat-trick early in the second period with Stuart Armstrong rounding off the scoring.
Speaking post-match, Grayson was left to stew on what was a hard afternoon of football in his first home match in charge.
"We had a meeting a one o'clock today and we gave the players a list of things we wanted them to do, to perform with the ball and without the ball," he said.
"And what is required from the players and what it means to the supporters and this football club.
"We are standing here now with all those things having gone out of the window.
"The one positive thing is we haven't lost three points but ultimately it is a reminder and a real kick up the backside to all, myself included, that there is a lot of work to be done both on and off the pitch."
He continued: "You have got to give Celtic a lot of credit, they are a real strong team and they have got some talented players.
"They are playing in Europe and their sharpness is better than ours and that is the only excuse I can give the players.
"When you allow any opposition the time and space to play, you give them easy goals like we have done it is very disappointing."
