Collins has controversially claimed the Parkhead side’s domestic opponents are “not clever enough or quick enough thinkers” to punish Ronny Deila’s men.
He said: “Sometimes, we switch off and think it doesn’t really matter, because they’re not going to punish us.
“If you become open and detached from each other against good players and good teams, you’ll be punished.
“It’s something that doesn’t happen to us in Scotland. No disrespect to the other Scottish teams, but they’re not clever enough players or quick enough thinkers to punish us.”
Collins made the comments in relation to how Celtic have to play a different style in European fixtures and how he feels opponents at home do little to help them progress on the continent.
Hartley has responded by dismissing the former Hibernian manager’s claims and told Sky Sports News HQ: “I think it’s unfair on the rest of the clubs in Scotland.
“I think it’s being disrespectful. We try our best. We haven’t got the budget of every other club and Celtic are way ahead of us but I think, on our day, we have shown we can give them a game.
“They have already taken three players (Dundee United’s Gary Mackay-Steven, Stuart Armstrong and Nadir Ciftci) from the Scottish Premiership, so it can’t be that bad.
“They’ll probably look at more players. Aberdeen ran Celtic close last year and just fell short. Aberdeen are strong, Hearts are strong. On our day, we have shown we can match them.”
Aberdeen boss Derek McInnes has also hit out at Collins, claiming Celtic would win a clean sweep of trophies if the difference in quality was as big as the 47-year-old said.
McInnes said: “He’s got a lot to say for an assistant manager, to be honest. He’s entitled to his opinion but if it was that easy, they would win the treble every year.
“I think it’s very disparaging, it’s a poor comment. There is a level of competition there that can test them and I think what he said is a slap in the face to the rest of the league.”