Sydney midfielder Isaac Heeney looks likely to miss Thursday night's important clash against Geelong at the SCG with concussion.

The Swans will give the gun youngster time to prove his fitness over the next couple of days, but he's not expected to do much training at the club's last session on Tuesday.

Heeney gathered just five possessions in last week's loss to Richmond at Etihad Stadium after copping a knock in the second term, and played virtually no part in the second half.

He was given a concussion test at the main break and passed all of those protocols but experienced some delayed symptoms during the third quarter and was taken from the field.

Along with the prospect of Heeney missing the Cats game, the Swans have already ruled out Tom Papley (hip flexor), Sam Reid (quad) and Lewis Melican (hamstring).