SYDNEY Swans coach Paul Roos says his side's three-game losing streak is set to continue unless its effort levels improve.

Coming off successive heavy losses to Geelong and the Western Bulldogs, the Swans were outgunned by Fremantle in the first half at the SCG on Saturday.

Despite a third-quarter resurgence from the home side, Freo held the Swans at bay to inflict their third straight defeat by 37 points.

"It is a concern, because you'd like to think that coming back on your own field, you'd have effort," Roos said.

"The most basic element of playing a contact sport is effort. If you don't have effort, you've got no chance to win. I was really disappointed in the first half.

"It's surprising, but clearly we've got to find an answer to that quickly because if you don't have effort, you'll get beaten by everyone."

The Swans' second-half comeback was hampered by a restricted bench after Tadhg Kennelly (knee) left the ground early in the first term and Daniel Bradshaw (knee) was gone by midway through the third quarter.

Roos freely conceded that the Swans had fallen significantly from their lofty spot atop the AFL ladder after six rounds, with injuries and form both contributing to the slump.

"We've dropped off a fair bit over the last three weeks. We've dropped off [in] personnel and then you lose Kennelly in the first three minutes [today]," he said.

"I think what we do know now is that we're just not a good enough team to cover five or six players and then play good footy."

As much as he was disappointed by the Swans' early lethargy, Roos was pleased with the contributions of first-year players Gary Rohan and Lewis Jetta.

Rohan finished with 15 touches, six tackles and a goal while Jetta bounced back from a quiet month with 17 possessions.

"The good thing was they actually got us back into the game … the bad thing is that they showed our senior players the way it should have been done," Roos said.

"The positive side of the injuries is that you get to see these guys and they're certainly improving."

He also praised rookie ruckman Mike Pyke, who rebounded from a shaky start against Aaron Sandilands to break even in the second half.

"Sandilands, early on, was pretty dominant but I thought after half time ... Pykie did a super job," Roos said.

"It was a really good effort to really nullify his early dominance. The way Aaron's playing at the moment, to keep him down to 10 possessions was a really good effort."