Roethlisberger is drawing from experience after 12-plus years in the league and multiple concussion-related issues.
"The brain is nothing to mess with," Roethlisberger told Indianapolis reporters on a conference call. "He is young and has a long career ahead of himself."
Roethlisberger, 34, said he has to expect Luck, 27, to play because Luck's a "tough competitor" and "one of the best in the game." But he wouldn't knock Luck for sitting if necessary.
The Tennessee Titans sacked Luck twice and hit him eight times in the Colts' win Sunday, with defensive tackle Austin Johnson's fourth-quarter hit likely forcing Luck into the concussion protocol.
Luck must be cleared before playing. Scott Tolzien is the backup. On the season, Luck is averaging 3.5 sacks per game.
Roethlisberger was in the protocol last season after taking a hit from Seattle Seahawks defensive tackle Michael Bennett in a Week 12 loss. He played the next game, with six full days to recover compared to Luck's three days this week. Roethlisberger said after that game that he didn't have a concussion. Roethlisberger has taken 453 sacks in his career, 34 in the past two seasons. Roethlisberger's concussion history dates to at least 2006, when he was questionable for a game with the Oakland Raiders while coming off a head injury.
When asked by Indianapolis media whether he's kept track of his concussions, Roethlisberger said, "I have no idea. Maybe too many."
"I have played this game a long time and younger days in my career when I wouldn't have [missed time], and there were many times that I've said that I haven't told anybody that I had been dinged or had a concussion," Roethlisberger said. "Looking back on it, I wish I wouldn't have. You have to be smart when it comes to your brain because you only play football for such a short period of your life. When you have a family and people that you are going to be with for the long term, you have to really make sure your health is taken care of."
Roethlisberger has played through several injuries as part of what he calls a "violent sport." One injury can't be played through, he says.
"You can rub dirt on a lot of things, but you can't rub dirt on the brain," Roethlisberger said.
ESPN's Mike Wells contributed to this report.