Friendships and allegiances will be put to the test when Fremantle take on Sydney with top spot on the line in Thursday night's blockbuster in Perth.

Fremantle's 14-game winning streak was brought to a surprise halt last week when they suffered an upset 21-point loss to GWS in Canberra.

Despite that defeat, the Dockers (14-2) remain premiership favourites, but Sydney (13-3) are nipping at their heels and will overtake Fremantle at the top of the table if they win by enough on Thursday night.

If Fremantle win, they will have a two-game buffer at the top of the ladder and all but seal a top-two berth and two home finals.

The stakes are big, and one man who will have conflicted feelings is Matthew Pavlich.

Pavlich bled purple during his glittering 353-game career at Fremantle, leaving his heart and soul out on the field in his ultimately failed quest to land a maiden AFL premiership.

But the 44-year-old is now the chief executive of Sydney, and Swans coach Dean Cox has no doubt where Pavlich's allegiances will lie on Thursday night.

"It'd be an interesting week for Pav, but he's red and white," Cox said on Wednesday while Sydney trained at Optus Stadium.

"You always have fond memories of the clubs that you spend time at, and no doubt he's got that at Fremantle with the time he spent there.

"But he's all in for the Swans at the minute."

Another interesting side plot is the coaching battle between Justin Longmuir and Cox.

Longmuir was an assistant coach at West Coast at the tail end of Cox's playing career, and the pair then spent a few seasons coaching together at the Eagles.

Earlier this year, Longmuir served as Cox's assistant at Western Australia during a State of Origin loss to Victoria.

Cox said he had learned a lot from Longmuir during his early coaching days, and has been impressed by what his mate is achieving at the Dockers.

"The good part about Justin is he was a bit more experienced than me, so he gave me a lot of his knowledge on how to handle situations," Cox said.

"Fremantle are playing a really process brand of footy, and that's exactly what Justin is.

"He's very strong on where he wants to get to, how he gets his players there, and he's doing well.

"We're probably both lucky to be in a position to coach two great football clubs."

With top spot and bragging rights on the line ahead of a potential re-match in the finals, Cox says his players will embrace the challenge of taking on Fremantle at a sold-out Optus Stadium.

"It's an amazing battle to be a part of - two teams that are in good form, and you get to do it in front of 60,000 people," Cox said.

"Our players are really excited for that. We get an opportunity to come over here and take on the best team. We can't wait for it."

Sydney will be boosted by the return of Tom Papley (calf), while Fremantle are set to be without star midfielder Hayden Young (groin).