Sportal.co.nz 26.Feb.2013Getty Images
Horwill, who missed the end of last season and the entire Wallabies campaign with a serious hamstring tear, injured his left ankle in a training mishap prior to his side's opening-round loss to the Brumbies.
The 27-year-old had originally planned to return in last Saturday's 25-17 triumph over the Waratahs but will have to wait at least one more week before making his long-awaited return.
"I won't be playing this week," Horwill, wearing a moonboot, said."It's been a little bit frustrating but [the moon boot is] hopefully coming off by Tuesday and then I can get back into it.
"We're hopeful I can get back in the next couple of weeks but we just need to see what the response is to running.
"I ran last week and pulled up a little bit sore so hence the reason I went back into the boot to try and de-load it a bit and take a bit of the pressure off while walking around."
The Wallabies captain is confident the injury is not worse than first thought and is confident his latest set-back will not threaten his dream of playing against the British and Irish Lions in June and July.
"I hope so, that's the plan," Horwill said when asked if he'll be fit and firing in time for the first Test in Brisbane on June 22.
"First, I just have to get on the field, it's been a long time off for me but there's still a lot of rugby to be played.
"We've only had two rounds of Super Rugby so there's plenty of footy to play and I'm hoping not to be out for too much longer but when I get back and make sure that I'm still playing to my ability that I know I can then we'll see where that goes from there."
Another man confident of returning in time for the 'once-in-a-career' series against the Lions is Reds and Wallabies half-back Will Genia.Genia tore his anterior cruciate ligament in Australia's Rugby Championship win over South Africa in September.
"At this stage hopefully round five or round six, the whole rehab process has gone really well and really smoothly," Genia said of his likely return date.
"I've also got to tick off a few boxes and start doing contact as of this afternoon so hopefully everything goes well."
But the 25-year-old is adamant he will not risk further injury by coming back too soon.
"I think it's really important [to be patient], not just for the Lions series but in terms of my well being as a player moving forward," he said.
"I spoke to James [Horwill] and spoken to a lot of guys who have done their knees previously and they said the worst thing you can do is try to rush back so I'll just go and if it feels right I'll play and if it doesn't I'll give it a few more weeks."