The 30-year-old defender is nursing a calf injury ahead of what would be his 500th appearance for the club, as the Robins look for the win that would seal promotion to the Championship.
Johnson said: "I don't know whether Louis will be involved yet to be honest. He has been for a scan and what we now know is it is not a muscle tissue problem but a nerve problem.
"Hopefully we can free it and take down the swelling a bit with some anti-inflammatories.
"He would need to be training by Thursday to have a chance so we will just have to wait and see."
Sporting Life