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Now the 23-year-old is considering a self-imposed and lengthy leave from professional rugby to address his alcohol problem once and for all.
It has been revealed Guildford left the Crusaders training camp voluntarily mid-last week after admitting he was involved in a drunken incident at a Christchurch house on January 12.
A source close to the situation told the Herald Guildford was drinking at the house "for a couple of hours".
He then left and went on a gambling and alcohol "binge".
Later that night Guildford returned to the party. The source said by then he was "completely out of control" and allegedly assaulted another partygoer.
Things were bad enough for Crusaders halfback and former All Black Andy Ellis to be called to help and he arrived at the party to help get Guildford under control. He took Guildford away from the party.
Ellis did not return calls yesterday.
Earlier in the night Crusaders players Tom Marshall and Kieron Fonotia, from the wider training squad, were also at the party. They had left by the time the alleged assault occurred.
The victim did not want to press charges, and police were not called.
However, a Christchurch police spokesman said an investigation could still happen if the incident was serious and if it was reported to police by "witnesses or interested parties".
The source said that although Guildford's alcohol problem had been widely publicised after three incidents in the past 18 months, the Canterbury Rugby Football Union also had concerns over his gambling.
Guildford's Auckland-based agent, Simon Porter, would not comment on whether the 23-year-old had a gambling issue. "There's been a pretty common theme whenever Zac's crossed the line and that's been with the alcohol - so that's his focus," he told the Herald yesterday.
He revealed that Guildford approached Crusaders coach Todd Blackadder last Monday and told him about the incident.
He is now "taking some time out" at an undisclosed location.
"As the week went on it became pretty clear that it wasn't in Zac's or the Crusaders' interest for him to be in the team environment. So the decision was made last week that he should spend some time away to concentrate on dealing with it," Mr Porter said.
In late November 2011 Guildford vowed to stop drinking for a year after he was arrested in Rarotonga for storming into a bar naked and drunk and punching two men.
After the incident Guildford also publicly apologised for his behaviour and said he wanted to focus on his rugby.
But before the year was over, Guildford was photographed drinking beer and claimed he had changed his ways and could trust himself to enjoy one or two drinks with friends.
"He had been working really hard since Rarotonga, so he's devastated. He knows he's let himself, his family and the Crusaders down.
"Why? I don't know. Why do you order another drink? It's just one of those things, he got drunk and just overstepped the mark I suppose ... of course he wishes he had made a different decision at the start of that day," said Mr Porter.
"Zac's gutted, because a lot of people have stood by him and supported him - and he's definitely not seeking anyone's sympathy. He just knows he's let people down and that's what hurts the most.
"You can't keep saying sorry, and he's dealing with that. That probably is the chief reason as to why the decision was made to take some time away. Given his history, he's pretty stressed out with the whole situation."
Mr Porter could not say how long Guildford would be "away" from rugby, but likened the situation to former Black Cap Jesse Ryder taking himself away from international cricket to focus on his own issues with alcohol.
"Zac's just having some time away. He's just trying to work out what to do. Last time around rugby was seen as the solution - staying within the environment. But that didn't work so well. So now just some time away from that environment might be better for him."
Mr Porter said Guildford would seek professional help for his drinking problem, and would likely give up alcohol permanently.
"I don't want to say something that's going to come back on us but I think it's fair to say his drinking career is probably over. It kind of has to be. But I think it's safe to say that he'd gone down a course, he was comfortable about where he was at and thought he could manage it, and that's backfired on him.
"It's probably likely that he's going to have to knock it on the head.
"I just don't know. I'm not the professional. If he knew why, I think it wouldn't have happened because he would have been able to stop it. In no way am I trying to trivialise it and I understand it's a massive issue. It's just a field I'm not an expert in."
Mr Porter said he would support Guildford getting treatment and dealing with his issues.
"I just want Zac to fulfil the potential that everyone knows he's got ... Does he want to keep playing? Absolutely he wants to. It's a privilege he hopes he can continue to have but that's in the hands of the NZRU now."
- Kurt Bayer, Anna Leask