Hembery had been scheduled to appear alongside Mercedes' Ross Brawn, Stefano Domenicali of Ferrari, Red Bull's Christian Horner, Martin Whitmarsh from McLaren and Sauber's Monisha Kaltenborn.
But with Pirelli at the heart of the test furore currently dominating Formula One, and ahead of an International Tribunal, Hembery appears to have felt it wise to withdraw.
Ordinarily non-attendance of an FIA press conference would be a breach of the sporting regulations, and likely incur a fine.
But motor sport's world governing body has confirmed that as Pirelli are not a team, and in light of the sensitive nature of the situation at present, it is highly unlikely any sanction will be imposed.
The FIA announced on Wednesday Mercedes face an International Tribunal after seemingly contravening the sporting regulations.
The hearing has been called after Red Bull and Ferrari protested Mercedes' use of a 2013 car to assist Pirelli in a 1,000-kilometre test, predominantly of next year's tyres, in Barcelona in mid-May.
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