The pair missed Melbourne’s round 21 loss to Port Adelaide at AAMI Stadium.
Sylvia flew to Adelaide, but was a late withdrawal due to illness and was replaced by traveling emergency Rohan Bail.
Macdonald (ankle) was a forced omission, when the initial side was announced last Thursday.
Both will have to pass fitness tests this week, if they are to play in James McDonald’s last match for the club.
Youngster Luke Tapscott will now be sidelined for round 22 and the rest of Casey’s finals campaign.
The first-year Demon reinjured his shoulder last week in the VFL.
As already known, Aaron Davey (leg), Jack Grimes (hamstring) and Ricky Petterd (shoulder) won’t be available.
Stef Martin (hip), Neville Jetta (shoulder), John Meesen (foot), Jordan Gysberts (back) and Max Gawn (knee) will also be unavailable for Casey’s finals campaign.
