conference the mercurial Mourinho had launched into one of the tirades against referees that keep his PR team so busy.
As we chat Greenberg's mobile rings constantly. Most worryingly,
The Sun is running a story on how Mourinho's comments have led to 'death threats' against the referee. Similar threats last year led to the retirement of Swedish referee Anders Frisk, but Greenberg is quick to check the facts and rebut the rumour.
Nevertheless he says this season is much calmer than the last, when newly appointed Mourinho was in the news on a daily basis. 'At the height I was taking 15 to 20 media calls a day; now it's more like five to ten. Since Chelsea have finally won the Premiership things feel less pressured.'
Late last year Greenberg recruited head of media Simon Taylor (PRWeek, 6 October 2005), enabling him to concentrate on more proactive communication. And he has just begun a major charm offensive to counter the club's image in some quarters as arrogant and aloof.
This kicked off last month when he lined up his boss, chief executive Peter Kenyon, for a number of national press interviews, prompting The Guardian to run the headline: 'Why Chelsea just want to be loved.'
'It was actually a case of some CSR projects – redeveloping the Linford Christie stadium in White City and a number of local children's initiatives – coming to fruition,' explains Greenberg. 'But I suspect we put more into CSR than any other British club.'
He refrains from revealing exactly how much ('people will just say "is that all [club owner and multibillionaire] Roman Abramovich will spend?"') but promises a CSR report at the end of this season. He says he hopes spend on community and charity initiatives 'will continue to grow'.
Despite the stated aim of becoming 'Europe's most successful club' by 2014, Abramovich and Kenyon recognise they need to balance ambition with a softer image. To this end they brought in Greenberg, an experienced sports hack, at the beginning of last season. Like Kenyon he was not a Chelsea supporter, and insists that while he has the job he will not watch his team Tottenham Hotspur play.
'There is a British tendency to knock champions and Chelsea are often accused of "buying" success, which time will prove to be false,' says Greenberg emphatically. 'We take a lot of criticism on the chin. And while we're not prepared to be a punch bag, I do worry about our reputation every day.'
His remit includes political relationships ('government and football establishment'), internal comms (the club has over 500 staff) and editorial products (Chelsea TV, match-day programmes, magazines and website).
Sitting on the executive board, which meets weekly, at just 36 Greenberg is effectively a corporate affairs director.
He does not see himself as a PR man however ('if someone asks I say I work for a football club'), and insists he has no idea where this career will take him. 'When I took the job it just felt right. It was the most exciting project in world of football and I wanted to be on board.'
The seven-day-a-week role eats into his personal life and, despite his sportsman's physique, Greenberg says he no longer has much time to play football himself. Indeed, he realises that he is only as good as the last press conference he runs. But he talks about Mourinho with the same fierce loyalty as one of Chelsea's players ('he's a hugely impressive person').
But when one sees the manager and Greenberg talking together, one is reminded of the way Tony Blair once leaned on Alastair Campbell. It is clear that the 'special one' values this robust media minder in much the same way.