McCann, who only took charge of the team for the first time on February 26, admitted it was a tough day after a 1-0 home defeat at the hands of Nottingham Forest condemned Posh to a bottom three finish.
But he expressed pride in his his players and his staff for their efforts since he returned to London Road.
"It’s a tough day for everyone,” McCann said. “It’s a sad day for the good people who work tirelessly behind the scenes and for the fans who part with their hard earned money at home and away games. We just haven’t been able to deliver for them.
“But after the game I thanked the players for their efforts in the 12 games since I’ve been here. Their determination, effort and attitude has been first-class. We’ve come unstuck in some games, but we went toe-to-toe with the best form team in the league today and lost because of a lapse of concentration just before half-time. We were the better team up to that point. The gameplan was working, but we missed our chance early on and then got caught by a sucker punch, and then it became difficult. We had moments in the second-half, but the ball wouldn’t fall for us.
"I now want the players to feel the pain and use it to their advantage next season. The comeback will always be stronger than the setback.
"In my time here I would love us to become a sustainable Championship club, but it’s one step at a time and next season we have to get out of League One.”
McCann suggested there would be no experimenting with players in the final two games at Millwall next Saturday (April 30) and at home to Blackpool on May 7.