Johnson told BBC Radio Cambridgeshire: "We asked him to take the meeting after training and tell us what he thought.
"He was quite angry and disappointed even though he was part of the team."
He added: "He's one of the leaders in the dressing room.
"What he came up with is probably what everyone else would have come up with but wouldn't have quite had the confidence like he did."
After being outplayed at Victoria Park, Johnson said he would bring the squad in for extra training and came good on his promise.
"The boys came in on Sunday morning, I felt we needed to do a lot of running," he said.
"It wasn't very scientific, it was to let them know it wasn't good enough.
"They've got to know that if it drops below a certain standard then they will be in running hard on a Sunday.
"They've probably never worked that hard in their professional careers on a Sunday."
Meanwhile Johnson confirmed the club will not be appealing against the red card handed out to Lee Tomlin at the weekend.