It is not only team management that has taken a dim view of Guildford's behaviour - some senior players believe he has abused the privileges that come with being an All Black.
His second drinking episode was at the team's Brisbane hotel after his disappointing on-field performance against Australia on August 27. The All Blacks lost that game 20-25.
Details of the incident have not been revealed but a week earlier, Guildford made undertakings about his drinking to the coaches at a meeting while the team were in South Africa.
All Black manager Darren Shand said the coaches had concerns about Guildford's drinking.
"He had some agreed expectations set for the rest of that tour about moderating his alcohol consumption through that period of that tour."
Yesterday, Guildford admitted he had a drinking issue."I feel I let myself down and the team down," a sombre Guildford said.
"Obviously a poor performance on the field in a week that I felt the pressure at times led to me making a few bad decisions off the field following that game."
Guildford is now on a "self-improvement programme" to address his drinking issues.
"I'm trying to make positive steps and improve as a person and I think that will lead to me being a better player."
Shand said the issues would not affect Guildford's selection chances. He has yet to play in a World Cup match.
Guildford was a contentious World Cup squad selection, and many critics felt the rejected Hosea Gear and Sitiveni Sivivatu had stronger claims.
After the Brisbane match, Shand met Guildford and his agent "and had a long discussion about his behaviour, particularly in relation to alcohol".
"Zac took a lot of personal responsibility that day," Shand said yesterday.
"Let's keep this in context. It was a minor incident - he breached an agreement with the coaches. He didn't breach any team protocols.
"We are really proud of the progress he has made since then. He has really taken ownership of it."
Shand said there had been a lot of speculation about the incident that was "just not true".
Guildford said: "I feel now that I have got a chance, and I want to make the most of it. I'm in the All Blacks now and I want to stay here. I don't want to throw this opportunity away."
The All Blacks are not subject to alcohol restrictions during the World Cup, but are expected to adhere to behaviour protocols.