NORTH Melbourne are undefeated and top the AFL ladder but defender Scott Thompson recognises there is still plenty of room for improvement.

The Kangaroos face St Kilda on Sunday with games against Essendon and Carlton to follow.

Based on those sides' current form, North will tackle the Sydney Swans at the SCG in round 10 with nine wins in the bank.

Thompson isn't looking beyond Sunday’s match at Etihad Stadium, where he will attempt to halt Saints captain Nick Riewoldt's run of vintage form.

The 29-year-old knows the Kangaroos must lift if they're going to extend an impressive start to the season.

"We haven't lost a game but we still haven't been playing our best footy," Thompson said.

"We haven't lost a game but we know there's a lot of room for improvement.

"If we keep playing the way we've been playing then we'll drop a few games.

"So we have to keep improving."

Riewoldt was best on ground in the Saints' last-start win over Melbourne and looms as the man most capable of ruining Drew Petrie's 300th game.

Riewoldt signed a one-year contract extension last November and is expected to announce he is playing on for another season soon.

Thompson was full of praise for the veteran forward.

"Nick's in awesome form at the moment. He has been the whole year," he said.

"He's probably back to his best, if not better.

"It's going to be a big challenge for our back group, they'll probably go in with three talls so we've got our work cut out for us."

Thompson implored North's entire 22 to play a small part in stopping the St Kilda captain.

"Hopefully the midfielders and forwards can help us out and put a bit of pressure on," he said.