"I'm practicing to play, if that tells you anything," Jackson said.
Jackson said he would have been no better than 50 percent efficiency last week at New England, when the thigh tightened during a pregame workout. He said the situation has improved every day this week.
"It's not 100 percent, but it's not something that's unbearable like Sunday where I wouldn't be able to be myself out there," Jackson said. "So we felt taking a week off would probably be the best thing for the rest of the season."
Coach Jim Haslett repeated his assessment from a day earlier, saying Jackson, defensive tackle Adam Carriker (sprained ankle) and defensive end Leonard Little (hamstring) all would be "50-50 game-time decisions." Little was likely the longest shot after taking no snaps in team drills.
Jackson, who leads the NFL with 127.8 yards from scrimmage per game, said he would save his stiffest test for game day.
"The test is Sunday," Jackson said. "You don't know if you go too hard on Friday, would it tweak it and frustrate things.
"If I had to tweak it, I'd rather tweak it in the game."
But so far, he's feeling better. Jackson ran several plays with the offense to get a taste of the Arizona defense and ran some pass routes.
Jackson has 508 yards rushing, a 4.2-yard average and four touchdowns and is the Rams' second-leading receiver with 25 catches and a 10.4-yard average. With Jackson out at New England, Antonio Pittman had 83 yards on 19 carries in his first career start in a 23-16 loss.
"It's very frustrating to sit out any time, especially a close game like that where you never know if I could have been the difference maker," Jackson said. "We just want to make sure everything is good and I can play at a level that can be positive."
Jackson said he wouldn't push to play just because the Rams (2-5) can make up ground against NFC West-leading Arizona (4-3).
"You go into a season trying not to miss any games," he said. "There's no doubt in my mind that if I'm not 100 percent, whatever we decide to do as a unit, my backups and the guys surrounding me on offense can pick up the slack."
The Rams are 2-1 under Haslett, who said he hasn't mentioned to players that they can cut the Cardinals' lead to one game.
"I haven't even brought it up," Haslett said. "I think they know it. I told them the environment's going to be great because our fans will be there. Enjoy that and take care of business when you can."