PERTH, AUSTRALIA - DECEMBER 18: Mitchell Starc of Australia looks on during day five of the Third Test match during the 2017/18 Ashes Series between Australia and England at WACA on December 18, 2017 in Perth, Australia. (Photo by Ryan Pierse/Getty Images)

Former Australian fast bowler Glenn McGrath believes Test star Mitchell Starc should return to the line-up for the fifth and final Ashes Test in Sydney, but only if he's 100% fit.

Starc missed the Boxing Day Test after struggling with heel problems following an incident during the third Test in Perth a week earlier.

The star paceman looked his normal self in the nets ahead of Day 1 on Thursday, and speaking to the media at the SCG on Tuesday, McGrath believes Australia should have their upcoming four-Test tour in South Africa in mind when deciding Starc's plans.

"You'd love Mitchell Starc to be playing, there's no doubt about it," McGrath told reporters.

"Someone who bowls at that pace, attacking lengths that he bowls and swings the ball.

"You want him playing every game possible, especially at his home ground here.

"But with a big tour of South Africa coming up … if he's 100 per cent fit I'd play him.

"If he's not quite there, unfortunately (they) might have to let him have a rest and have him ready for South Africa."

Starc was replaced in the Boxing Day test by Jackson Bird, although the 31-year-old struggled with the ball, and finished with figures of 0/108 from 30 overs.

Australia's four-Test series against South Africa begins on March 1, meaning Starc would have to wait another two months before returning to the Test arena if he's left out of the Sydney Test.

Starc's teammate Pat Cummins also spoke to media on Tuesday, and believes Starc is confident he'll be cleared to play on Thursday.

“I haven’t spoken to him but it looked like he was bowling quick, running around and wasn’t limping,” Cummins said.

“I know he’s really keen to play and he’s pretty confident he’s going to play.

“Now it’s seeing how it recovers. He said it’s got better the last week or two since Perth. So hopefully he gets through today and he’s alright.”