Sam Kerr is OUT of Australia's first two matches due to calf injury in training

Sam Kerr has been ruled out of Australia's opening World Cup game and their second group matches after sustaining a calf injury.

The news comes as a huge blow for the Matildas, with Kerr both their captain and star striker.

The Chelsea forward was filmed smiling as she got off the team bus and walked into the dressing room but was not named in the matchday squad to face the Republic of Ireland.

Kerr posted on Instagram: 'Unfortunately I sustained a calf injury yesterday in training.

'I wanted to share this with everyone so there is no distraction from us doing what we came here to achieve.

'Of course I would have loved to have been out there tonight but I can't wait to be a part of this amazing journey which starts now. Sam.'

The Matildas official twitter account said Kerr will also miss their second game with Nigeria on July 27.

'Sam will be unavailable for the next two matches with the Matildas Medical Team to re-assess her following our second group stage match.'

Australia's final group match is against Canada on July 31.

There were telltale signs that something was afoot with the Chelsea star when fans failed to spot her on Australia's team walk in Sydney on Thursday morning.

Kerr's teammate with the Matildas, Elise Kellond-Knight, said she is heartbroken for the superstar player after the bombshell news.

'My heart really breaks for Sammy,' Kellond-Knight, who is nursing her own achilles injury, said on Channel Seven. 'I know she wants to be out there, I know she wants to be a part of these two games.

'Luckily there's another 22 players on this team. The team isn't just Sam Kerr. We saw that on Friday night, so I think we can all be really confident that we can go into this game with plenty more opportunities where we're going to create really good attacks.

'I think for the average fan out there, they'll be shocked. I mean, a lot of people only know Sam Kerr for the Matildas, but I can guarantee you there are a lot of superstars in this team and I don't think we need to be worried or concerned at all going into this game.

'We've got so much depth. If anything, it's kind of great that we can rest Sam and afford to put her on the sidelines and then look at our other players and create our attacks through those players.'