"It happens all the time," Haslett said. "You can run all you want, you can lift weights all you want, but until you put pads on and you actually cut and move at full speed, you can't replicate that until you actually do it."
Haslett noted it's the same in any sport, that the body needs time to adjust.
"That goes back to when I was playing," said Haslett, a former NFL linebacker. "Guys that don't go to training camp get hurt."
Jackson will miss his fourth game in five weeks when the Rams (2-8) play the Bears (5-5) on Sunday. He disagreed Thursday with Haslett's blanket assessment, countering that injuries are bound to occur to players who take a pounding.
Jackson didn't report this season until Aug. 21 after getting a six-year, $44 million deal. But he pointed out he attended training camp in 2007, yet still missed four games with a bulging disc in his back and a torn groin muscle.
"Coaches bring that up all the time," Jackson said. "I think the football season is long and gruesome, and you have freak injuries like this. This injury wasn't from any hit, it was just that my muscle gave way."
Jackson said doctors told him the injury was not preventable, and that the best way to get back on the field is to do rehab and be patient.
The 6-foot-2, 235-pound Jackson is the Rams' leading rusher with 525 yards, a 4.1-yard average and four touchdowns. The Rams have lost four in a row since Jackson was hurt near the end of a 34-14 victory over the Cowboys on Oct. 19, one play before Haslett said coaches were going to take him out.
Jackson tried to come back after one week and wasn't himself. He didn't start against Arizona on Nov. 2 because the first play required a cutback he wasn't comfortable making, and totaled 17 yards on seven carries and dropped a certain touchdown pass before sitting out much of the second half.
The next two games he was a question mark all week. Haslett ruled him out for the Bears game on Monday after Jackson got a second medical opinion that he said revealed a more severe strain that doctors believed may have come from reinjuring the thigh against the Cardinals.
In an effort to prevent further soft-tissue injuries, Haslett wants Jackson to consult with strength coaches and nutrition experts in the offseason. While joking that "I think Mama Jackson does a good job," Jackson said he'll do what's necessary.
"I'm definitely open to explore all doors or all different types of training," Jackson said. "I want to be the best at my position and I want to be on the best team in the National Football League, and I hopefully want to lead the St. Louis Rams to the Super Bowl and a playoff berth."
The Rams are likely to bring in another running back next season, just in case Jackson gets hurt again. He won't mind that, either.
"You can bring in any running back and I'm going to beat him out, and I'm not going to share my carries," Jackson said. "I understand they have to have an insurance policy, but that's just my mentality."