Johnson had to be helped from the ground and is in the hands of trainers to determine the severity of the injury.
Swans football boss Tom Harley confirmed to Chanel Seven’s Daisy Pearce that “it looks like an ACL.”
Johnson returned last week having not played for six years after dealing with a host of injuries, including five knee reconstructions.
"It looks like an ACL."
— AFL (@AFL) August 12, 2018