"I've got to go back and check this guy more," Mayock said.
Dawson didn't stand out in drills, either.
"His instincts and quickness -- he was just phenomenal on tape," said Mayock, who later noted that once some players put the pads on, they showed their true ability.
However, Dawson was having none of it after his workout and took to Twitter to respond to the criticism of his showing.
Dawson led TCU with 136 tackles during the 2014 season, when the Horned Frogs (12-1) finished eighth nationally in scoring defense and 18th in total defense.
Mayock had touted Dawson's "instincts and toughness," saying, "I watched him for two hours and just laughed. He was so good."
TCU uses a 4-2-5 set, and Dawson is seen as an inside linebacker by some analysts and an outside guy in a 4-3 set by others. Mayock had called him a "true three-down linebacker."
NFL Media draft analyst Lance Zierlein also noted Dawson's struggles in Indianapolis, tweeting that Dawson's combine workout threw "a monkey wrench" into his draft stock.
Top inside linebackers Benardrick McKinney of Mississippi State and Denzel Perryman of Miami also had somewhat disappointing 40s. McKinney (6-4 1/8, 246) ran a 4.66, while Perryman (5-10 3/4, 236) ran a 4.78. "I thought he was faster," Mayock said of Perryman, though Mayock also said, "I still like Perryman," despite the slower-than-expected 40 time.
Perryman is a throwback of sorts, as he is known for his big hits and physical nature rather than his freakish athletic abilities. But his lack of height was bothersome to some teams, and now his 40 time could give other teams pause, as well.
As for McKinney, his size is a selling point, but Mayock and fellow analyst Daniel Jeremiah noted that McKinney wasn't as productive as you'd might expect.
"He's around the football, but didn't make as many plays as you'd expect," Mayock said.
Jeremiah called McKinney "a true flash player," saying the more tape he watched, "the more I got concerned." He also wondered about McKinney's football instincts.