Johnson's hit on Kennedy in a spiteful first quarter soured the Giants' stirring six-goal win over their cross-town rivals, with the All-Australian Swan helped from the field after being collected by Johnson's left shoulder off the ball.

Kennedy left the ground with concussion, but returned midway through the second quarter.

Ruckman Shane Mumford is also facing a nervous wait after a sling tackle on Kurt Tippett in the second quarter. Tippett had also been forced from the ground with concussion after copping an accidental knee to the head earlier in the game.

Any suspension to either Johnson or Mumford would rub them out of a home preliminary final against Hawthorn or the Western Bulldogs in two weeks.

"The game goes helter skelter and you just sort of go a hundred miles an hour watching the next moment, the next minute, the next five minutes so I haven't seen it," GWS coach Leon Cameron said of the Johnson bump.

"Until I have a look at that piece of vision, it's hard to comment. One thing I will say is he's obviously passed his concussion test and he's come back on and played the rest of the game.

"I thought the game was played in the right spirit. When there was a contest to be hit hard I thought our boys did it well and so did the Swans."

Johnson hasn't missed a single game through suspension since joining the Giants despite his chequered disciplinary history.

Just last week Johnson said fellow small forward Devon Smith had approached him before the club's round 23 win over North Melbourne and asked him not to get suspended on the eve of the finals.

The former Cat had an off day with the boot against the Swans, kicking five behinds and no goals.

Key forward Jeremy Cameron stepped up instead, booting four majors including one devastating burst of three goals in five minutes in the third quarter.

"The moment did come in the third quarter and he stood up and put a little gap for us going into three-quarter-time," Cameron said.

"It was neck and neck it was anyone's game really, it was a one-point difference at quarter-time, it was a two-point difference at half-time.

"He had a few shots, he's normally a really straight kick for goal, no doubt that swirling breeze really hurt him at times.

"His defence has come through in leaps and bounds this year. He tackles well, he's always courageous and hits hard.

"We're rapt with his game."

Cameron said his side would prepare for the preliminary final the same way they tuned up for the Swans game.

"We take our two weeks break, it's the unknown, we have to prepare like we prepared for this game because someone will beat us in the prelim final if we do not come with that same sort of attitude," Cameron said.

"There'll be surprises. In no way means do we actually look at it and say we're in the box seat.

"You never write off the Hawks, you never write off the Swans so what's going to happen over these next three weeks is going to be intriguing."