If the Lions dodged a bullet in the first Test against the Wallabies – had Australia been blessed with a goal-kicker worthy of the name, they would almost certainly have won – the home team evaded a disciplinary cannonball yesterday when James Horwill, their hugely influential captain, was cleared of stamping on the face of Alun Wyn Jones, his rival lock. Had Horwill been banned, the Lions would have been overwhelming favourites to win the series. Now, the outcome is not so clear.

To make matters worse for the Lions ahead of the second Test in Melbourne on Saturday, there are worries over the fitness of two of the tight forwards who imposed themselves on the Wallabies at the weekend. The England loose-head prop Alex Corbisiero, called into the squad after both Cian Healy and Gethin Jenkins picked up tour-ending injuries, has a damaged calf muscle. In addition, the experienced Ireland lock Paul O'Connell suffered an arm injury during the 23-21 victory two days ago and is under assessment.

Warren Gatland, the Lions' head coach, did not send for second-row cover, but he called up the Irish prop Tom Court for tomorrow's contest with a strong Melbourne Rebels side – the final midweek game of the trip. Court, born in Brisbane, was here on holiday, and will sit on the bench, thereby removing from the dirt-trackers' equation Mako Vunipola, who should start against the Wallabies if Corbisiero fails to recover.

The last thing Gatland felt he needed after receiving the latest injury bulletin was to risk the exciting Saracens forward against the Rebels.

Gatland and the Lions hierarchy alerted the authorities to Horwill's alleged misdemeanour after watching footage of a third-minute incident in which the Queenslander's right boot caught Jones in the face as the Welshman lay prone and defenceless at the bottom of a ruck. Jones required a couple of stitches to a wound near his left eye.

"Our feeling after the game was that the citing officer needed to have a look," said Gatland, who, as a former All Black hooker, was raised in the toughest of rugby schools. "I played in the age of rucking and still have scars to prove it, but even then the head was sacrosanct. You steered clear of that part of the body."

On the evidence of the available footage, Horwill appeared to have a serious case to answer. Indeed, some Australian pundits assumed he would be found guilty and banned from the remainder of the series, and then some. But after three hours of examination, the independent judicial officer Nigel Hampton QC, a New Zealander, decided the citing could not be upheld.

"I could not find that when James Horwill's right foot came into glancing contact with Alun Wyn Jones' face, he was acting recklessly," Hampton said in a statement. "I found that I could not reject as implausible or improbable Horwill's explanation that as he was driving forward with his right leg raised, he was spun off balance through the impact of Lions players entering the ruck from the opposite side."

It was Hampton who cleared Healy of a biting charge following the Lions' first game in Australia, against Western Force in Perth a little over three weeks ago. While the tourists are unlikely to be as satisfied with this latest verdict – there is a long history of British and Irish discontent with the disciplinary process during major tours of the southern hemisphere – the Wallabies will be mightily relieved. Horwill verges on the irreplaceable as the man who holds their pack together.

Robbie Deans, the Wallaby coach, added three players to his squad yesterday following the rash of injuries that affected his side so badly in the first Test. The full-back Jesse Mogg, a key figure in the ACT Brumbies' victory over the Lions in Canberra last week, and the centre Ben Tapuai, who performed strongly against the tourists for Queensland Reds, were summoned, as was the 32-year-old flanker George Smith, who played against the Lions in 2001.

Meanwhile, Tommy Bowe, the Ulster wing, will be considered for Test duty in Melbourne after recovering from the broken hand he suffered against the Reds. Manu Tuilagi, the England centre, is also fit following shoulder issues and will face the Rebels in a strong midweek side led by his red-rose colleague Geoff Parling, who played the last 10 minutes of the Test.

Sean Maitland, Owen Farrell, Richard Hibbard, Dan Cole and Dan Lydiate, who were on bench duty on Saturday, will start tomorrow.

Should the lions change a winning side?

Twelve years ago, Graham Henry changed a successful side for the second Test by rejigging his back row. It was too clever by half, and the Lions lost. Despite the precedent, Warren Gatland will be tempted to tweak things for this weekend's match.

Right wing

With the Ulsterman Tommy Bowe available after his super-fast recovery from a broken hand, Gatland could throw him in at the expense of Alex Cuthbert. This would be tough on the Welshman, whose high-class finish in Brisbane saved the Lions, but Bowe is undeniably the quality wing of the two.

Outside centre

England centre Manu Tuilagi has also avoided an early flight home. Now the human bowling ball's shoulder is up to scratch, a destructive performance against the Melbourne Rebels will set Gatland thinking. A solution is a seat on the bench ahead of Sean Maitland.

Back row

Can England flanker Tom Croft and Ireland No 8 Jamie Heaslip coexist in the same loose unit with their similar skill sets? This could be a chance for Toby Faletau, Sean O'Brien or the hard-tackling Dan Lydiate, above. A delicate call.