Johns, 23, ruptured his anterior cruciate ligament while playing for Essendon's VFL affiliate Bendigo at Port Melbourne last month.
His manager Peter Jess said investigations were being conducted to determine whether the hardness of the playing surface at Port Melbourne was to blame.
"What we've got to find out is whether in fact it was a safe workplace," Jess told the Nine Network's AFL Footy Show.
"That's one of the issues that we need to find out.
"We've been to the (AFL Players' Association), we've asked them to go check the ground and at this stage we don't have a final result on that.
"If it's found that it's not a safe workplace, then I would think that's probably going to be a thing that we'll follow up."
