Clarke says sorry while Katich a doubt for Perth

Sorry is the hardest tweet. Michael Clarke apologised via his Twitter feed for not walking after his last-ball dismissal sealed another calamitous day for Australia. While the vice captain was admitting that his "emotions got the best of me", Simon Katich was heading for hospital amid home fears that he could be forced out of the third Test.

Katich injured his Achilles while fielding during England's mammoth first innings but still opened the Australian batting, making a characteristically gutsy 43. But after he fell to Graeme Swann, the 35-year-old was dispatched to hospital for a scan. "It doesn't look good," admitted Michael Hussey. "It was an absolutely inspirational performance really. He's willing to show that he'll fight all the way even though he is on one leg, even the way he played today I thought he played really well considering he was obviously in a lot of pain. I even asked Ricky [Ponting] if he wanted me to open the batting and Kato said 'Nup'. He wouldn't have a bar of that either – [he said:] 'It's my job, I've got to do it'."

Katich's opening partnership with Shane Watson has been a rare secure part of a struggling side and there are few obvious candidates to replace him. Phillip Hughes, who began the last Ashes series in England with such high hopes, is currently averaging less than 30 in the Sheffield Shield and was overlooked for the 17-strong party announced ahead of the first Test. Another option would see Hussey promoted to open and Usman Khawaja given a Test debut – in a pivotal Ashes Test on what is expected to be the quickest surface of the series at the Waca in Perth.

Khawaja was originally called up as cover for Clarke and his troublesome back. There were no signs yesterday of the problem restricting the Australian vice-captain as he scored freely until that fateful last ball.

"I could tell in Michael's body language that he thought he was out," said Hussey after the close of play. "He's pretty distraught at the moment. He played awesome cricket – the way we have loved watching him play over the last few years. It was great for him to play that well but it was disappointing he couldn't get through to the end of the day. He's pretty shattered."

A few hours later, Clarke held his hand up for not walking and needing an England referral to dismiss him after Tony Hill's not out verdict. "Just want to apologise for not walking off the ground tonight when I hit the ball. I was just so disappointed, my emotions got best of me," he tweeted.

Andrew Strauss's captaincy has come in for some criticism from Shane Warne, but Hussey felt the introduction of Kevin Pietersen as the batsmen's thoughts turned towards the close of play was a cute ploy.

"Sometimes when someone's having a great game, it's not a bad idea to give them a chance with the ball as well," Hussey said. "Sometimes they can pull off something special – like he did today."

It left Swann more than happy to be temporarily upstaged by Pietersen's part-time off-spin to end the 104-run stand for the fourth wicket. He said: "It is sod's law – but I love sod's law sometimes. It's a massive bonus for us. Sometimes you need a bit of inspiration and who better to deliver it than KP? We love KP, especially when he's got a double century and gets their best player of spin out."

But there was plenty of praise for Swann too. Hussey, a former county team-mate and one of the foremost players of slow bowling in the game, had prospered against Swann in Brisbane but was impressed with his comeback in Adelaide.

"He's definitely improved out of sight since I played with him at Northamptonshire," said Hussey. "I remember he'd bowl these amazing deliveries, and then just let the pressure off with one or two bad balls an over. Now he's on the money all the time, hardly bowls a loose ball."