Neither Tippet nor Naismith made the trip over to Perth with the rest of the team, with both set to undergo fitness tests on Wednesday.
Sinclair has made the trip and is ready to play should one of the pair not be ready for the game.
“(Tippett and Naismith) are both a chance to come over but we do have Cal Sinclair over here already,” Sydney defender Nick Smith said after arriving at Perth airport on Wednesday.
“It might be something the coaches are concerned about, but I think it will be fine.
“If that’s the way it falls with Cal (Sinclair) doing the role without those guys, he’ll definitely be looking forward to it.
“He has been in and out of the side a bit but it gives him a big opportunity if that’s the case.”
Sydney has won nine of the last 10 matches against the Eagles.