The left fielder injured his right hamstring when he ran in to catch Will Venable's fly ball to end the disastrous seventh inning against the Padres on Sunday.
Jackson will be examined in Phoenix on Monday, but neither he nor manager A.J. Hinch sounded overly optimistic about his chances of being in the lineup against the Cardinals.
"I don't think Conor's going to be able to go," Hinch said. "We'll know more [Monday]."
LaRoche, who has not started the past four games with a right quadriceps muscle issue, pinch-hit and struck out looking to end Sunday's game.