Elliott Dickman felt his Sunderland Under-23 side deserved more after going down 1-0 to Manchester United at Hetton.
A Demetri Mitchell penalty three minutes into the second half proved enough to win the Premier League 2 contest.
Dickman said: "I’m disappointed that we lost the game because I didn’t think we deserved to. We used the ball well but we gave a cheap goal away.
"We didn’t create a lot to shout about but we did work hard and made it difficult for them, on the ball we passed it well but we do need to take more care in the final third."
There were no first team players involved with the first team training at the Academy of Light ahead of the visit of Bolton Wanderers on Tuesday.
Josh Maja sat out the game but is expected to return to first-team training this week.
Sunderland Under-23s are back in action Thursday lunchtime at Eppleton CW, they host Exeter City Under-23s in the Premier League Cup (KO noon).
Dickman added: "We have to dust ourselves down after losing and we will be ready and raring to go on Thursday."