Manager Tony La Russa said Harrison (back) will be held out of the lineup Thursday against the Mariners, James Fegan of The Athletic reports.
Harrison was pulled from Wednesday's contest due to lower-back stiffness and will sit out Thursday, though La Russa also indicated he could be convinced to include the veteran infielder in the starting nine. Regardless, it doesn't appear to be a serious injury for Harrison, and he should rejoin the lineup within a couple days if he is indeed out Thursday.