Tuqiri, a member of the 2003 Wallabies side that lost to England in the World Cup final, recorded a blood-alcohol reading of 0.05 when breath-tested by Australia's team doctor at 1.30pm on Monday.
But the Fiji-born wing insists poor time-management was the real reason he missed the session.
"It was just a bad read by me; I didn't read my diary properly... I failed to turn up at the time (of the) session and I thought I'd done (it) the day before," Tuqiri said.
"Obviously I'm not happy with not playing and letting the boys down in that sense, and also family, and the fans."
A sheepish Tuqiri appeared noticeably shaken as he fronted the media on Tuesday and expressed his disappointment at missing the chance to play alongside two of Australia's Test greats in their farewell match on home soil in Sydney on Saturday.
"Missing out on being selected is massive," he admitted. "This week Greges (George Gregan) and Bernie (Stephen Larkham) are playing their last (home) game and it would have been nice to play with those guys.
"I understand where they (Wallabies team disciplinary committee) are coming from and everything else; the fact that I did miss that session, I just didn't know it was on and I just thought something else was on, and it was missed."
Wallabies coach John Connolly revealed another un-named player was also breathalysed but registered a reading below 0.2 - the acceptable limit as agreed to by the players.
Tuqiri was on a suspended sentence following an incident in Cape Town on July 27, 2005 when he had an altercation with team-mate Matt Henjak after Henjak apparently threw a drink over him at a bar.
"The agreement that no off-field indiscretions were to occur for two years has been broken and there is no alternative but to impose a two-match suspension," Australian Rugby Union chief executive John O'Neill said.
Brumbies winger Mark Gerrard will replace Tuqiri for Saturday's blockbuster against the Springboks at Telstra Stadium.