Jarrod Bowen gave the Tigers the lead at Brentford after the break but Watkins’ bundled leveller ensued a 1-1 Sky Bet Championship draw at Griffin Park.
McCann said: “We are very disappointed because it was clearly offside as people will see when they watch it back. It took the gloss off what was otherwise a complete performance from the boys.
“I thought we were outstanding from start to finish, against a team everyone expects to be in the top six at the end of the season, and I’m sure they will be.”
Hull missed chances to seal the points when Tom Eaves fired just wide and Kamil Rosicki hit the outside of the post with a curling free-kick around the wall.
However, McCann continued: “It’s been a good boost this week and a performance like that will only add to that feeling, which is always good at this stage in the season. It will give us a great lift.”
The Tigers boss was also full of praise for 20-year-old sub Leonardo Da Silva Lopes, whose neat pass found Bowen in space to break the deadlock.
McCann added: “He’s got those type of passes in him and I thought he did really well when he came on.
“But overall that was an excellent team performance, definitely our best of the season so far.”
Brentford head coach Thomas Frank urged patience after his side’s search for their first home win of the season continued.
He said: “I am disappointed with the goal we gave away but I am 100% sure we will only get better and better and better throughout the season.
“We have to be patient but I am impatient like the fans and want it to be clicking as soon as possible. But the managers, coaches and players will keep coaching, working hard and reflecting until it comes.
“How long will it take? Hopefully four days, before our next game.”
Frank dismissed McCann’s offside claim for the equaliser, insisting: “For me it was a beautiful goal, a striker’s goal and if you’re going to start giving those for offside then the game will suffer.
“There’s a lot Ollie needs to learn in that role but he’s scored two goals in two weeks and both showed to me that he has a striker’s instinct.”
Brentford fielded five new players in their starting 11 and Frank insists it will take time for them to gel and start playing the high tempo incisive football his side have become known for.
He added: “We weren’t satisfied with the first half. There were 10 or 15 situations that were bad but the second half we had a much better tempo, created chances and had more quality in the final third:
“We showed more hunger and desire and had some massive chances that on another day go in and we win.”