In a low-quality encounter the Tigers had slightly more of the ball but neither team made enough of it, and when Matt Ingram spilled a weak Lee Buchanan shot in the second half, Derby debutant Sam Baldock was able to score the game's only goal.
Hull were pretty anaemic.
"We weren't ourselves, we were very safe, we didn't pass the ball quickly enough, we didn't break the lines quickly enough, we didn't pass forward quickly enough," commented McCann.
"When we went forward we didn't look threatening and we know we are threatening, we just didn't get that going.
"There's going to be games this season where that's going to happen but the very least we should come away with is a 0-0.
"We know we weren't at our best and it was a sloppy goal for us to concede, a mistake.
"If I look at the two home games we've conceded off three mistakes. It shouldn't happen and it's cost us.
"I just want my group to start believing in themselves because they're a very good group and they're at this level for a reason. We don't want to be here just to make the numbers up."
Asked what his side was lacking, McCann replied: "Just the last bit, the last little bit, putting the ball in the back of their net. We just didn't look threatening.
"I don't think the (Derby) keeper (Kelle Roos) had a real save to make and that's not like us, we're usually good in that aspect."
McCann was probably right in his assessment but it seems surprising Hull are lacking in belief after a barnstorming 2021-22 when they deservedly won the League One title, and a 4-1 win on their first day back in the Championship. They lost their second game 3-0 at home to Queens Park Rangers but the scoreline was deceptive.
Whatever the reason, Hull need to shake themselves out of it.