Watson has played for Australia in limited-overs internationals

But Brett Lee, who has been Australia's 12th man in the past eight Tests, has been released to allow him to play in domestic first-class competition.

"We feel it is important for Brett to get some solid match practice," said chairman of selectors Trevor Hohns.

Australia have used the same team in all four of home Tests this summer.

Middle-order batsman Darren Lehmann is under pressure to retain his position in the lineup after scores of 12, 5 and 11 in the previous two Tests.

Captain Ricky Ponting has defended Lehmann's form with the bat but the inclusion of MacGill and Watson in an expanded 13-man squad is a sign the selectors are considering a change.

Watson is an all-rounder who has already represented his country in limited-overs internationals.

MacGill is a proven performer with an outstanding record at the Sydney Cricket Ground, Australia's most spin-friendly wicket.

"Stuart gives us the ability to play two spinners if needed," Hohns said.

"Shane gives us the option of going into the match with a combination of two fast bowlers, two spinners and a seamer."

Australia won the first Test in Perth by 491 runs then the second in Melbourne by nine wickets to take an unbeatable 2-0 lead into the final match of the series.

Australia squad:

Ricky Ponting (captain), Adam Gilchrist, Michael Clarke, Jason Gillespie, Matthew Hayden, Michael Kasprowicz, Justin Langer, Darren Lehmann, Stuart MacGill, Damien Martyn, Glenn McGrath, Shane Warne, Shane Watson.