Johnson hurt his knee in the win over Essendon last Friday and was last night operated on for a miniscal tear and will resume training in the week before the match against Adelaide on July 2.
Better news for the Cats last night was the downgrading of the penalty against Jimmy Bartel from one match to a reprimand by the AFL tribunal.
"It's a shame for Steve, he was just starting to get quite a level of fitness behind him,'' Geelong training services manager Steve Hocking said last night.
"He played out the game and and after he cooled down it swelled up on him. It's been cleaned up and while it's disappointing for him, a good result is that the break falls in the time he'll be out so hopefully he should be back after three matches.''
Johnson kicked three goals against the Bombers, but the injury continues an up-and-down season for the forward.
He suffered more ankle trouble during the pre-season and was dropped for rounds near the end of April.
Meanwhile, Skipper Steven King will be tested after missing the past two matches with a calf injury and defender Jarad Rooke also faces a test on his foot injury.
Utility forward Charlie Gardiner will also be tested after an ankle ligament strain, while Peter Riccardi, Tom Harley and Tim Sheringham are all at least a further week away.
The Dockers also have their injury worries and will be without Peter Bell, Antoni Grover, who injured his shoulder against Western Bulldogs, and Graham Polak, who injured his groin.
Justin Longmuir will be tested for a knee injury.
At the tribunal last night, Bartel pleaded guilty to rough conduct against Essendon's Damien Peverill but successfully had the contact downgraded from reckless to negligent and is is eligible to play Fremantle on Saturday.
Kangaroos' Jade Rawlings did not have Bartel's success at the tribunal and was suspended for one game after he also contested a rough conduct charge.
Rawlings attempted to have his high bump on Richmond's Richard Tambling downgraded from reckless contact to negligent, but the tribunal jury agreed with the match review panel's original ruling.
