ISAAC Heeney is in doubt for Sydney's crucial clash against Geelong next week after suffering a delayed concussion against Richmond at Etihad Stadium on Thursday night.

The young midfielder appeared to cop a knock midway through the second quarter, but returned to the game to see out the half.

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He started the third quarter on the field, only to come back to the bench midway through the term, when Sydney officials ruled him out for the rest of the match.

Sydney coach John Longmire said Heeney had been tested for concussion at half-time and been cleared.

"He was fine at half-time but a lot of the time those head knocks aren't black and white, it can happen a bit later in the game," Longmire said after the match.

"While he was fine at half-time, I think he got a bit worse in the third quarter so we just stopped him."

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The Swans host Geelong at the SCG next Thursday night, a match-up against a fellow finals contender they will be desperate to win.

Heeney would be a significant loss if ruled out.

One of Sydney's most promising young players, he had averaged 22 possessions in 13 games this year and kicked 12 goals before Thursday night's match.

The Swans will also be sweating on the availability of Lance Franklin, who could come under scrutiny from the Match Review Officer for lashing out at Alex Rance.