Harbaugh's answer was blunt.
"If you're not dressing, it's because you're not good enough yet," Harbaugh said. "That's a fact."
Apparently, things have changed a bit since then.
Kindle was active and in uniform for Sunday's game against the Colts, which marked just the second NFL game of his career and first since a Week 4 contest against the Jets in which injuries forced him into action.
The former University of Texas linebacker was a part of the Ravens' kickoff coverage, punt return and kick return units on Sunday, and also got a chance to see some defensive snaps late in the game with the game out of reach.
He didn't record any tackles and admitted his pass rush wasn't as strong as it could have been, but seemed pleased with his play following the game. After watching the game tape, Harbaugh said he was proud of Kindle's effort, as well.
"Sergio did a nice job on special teams," Harbaugh said. "He was very solid. He got all of his blocks. He covered kickoffs very solidly. In the pass-rush stuff, he didn't really get on track. He was in that last drive. I think he was playing a little more conservatively. He can definitely crank up that pass rush a little more."
Kindle was taken in the second round of the 2010 draft, but suffered a fractured skull last summer when he fell down a flight of stairs. He sat out all of last season, but was cleared for contact this training camp, and has slowly been working his way back into the mix on the Ravens' special teams units.
So why was Kindle activated on Sunday after sitting out all but one of the Ravens' previous 12 games? What specifically had he done in recent practices which led to his activation?
"He just has a better understanding now," Harbaugh said. "I think in some ways, he started over from a football standpoint. He had been out for so long, and then the injury maybe had some kind of an effect. But he's been working very hard and he's been studying very hard. I credit (outside linebackers coach) Ted Monachino; he's done a great job with him - just some learning technique things he's done with him, kind of one-on-one type stuff. Also (special teams coordinator) Jerry Rosburg has him out at practice, after practice, every day doing extra stuff."
Kindle still has a ways to go. He suffered fairly significant hearing loss in his left ear as a result of the head injury, and is still trying to adjust to the NFL level of play, both on a physical and mental level.
But he feels that he's made progress as this season has gone along, and knows he's a better player today than he was the last time he stepped foot on the field on a gameday.
"That has to be it," Kindle said. "They won't put you out there if they don't think you're prepared. So yeah, I guess it's everything. I know I've been working my tail off. So it's evident that I've progressed from the Jets game to now."
"He's made a lot of progress," Harbaugh said, "and we think he's ready to play more and more."