Wasps and England turned to the local Health Protection Agency to help confirm the diagnosis, which is expected after Sackey underwent saliva tests.
England, who meet again on Monday ahead of the tournament opener against Wales on February 2, are also sweating on the fitness of lock Simon Shaw and scrum-half Peter Richards.
Shaw is waiting on the results of an MRI scan on the ankle injury he sustained in the defeat to Munster at the weekend.
The Wasps lock was hobbling around Twickenham on Sunday but is confident the injury is not as bad as first feared.
Richards saw a specialist after injuring tendons in his left bicep during London Irish's European Cup win at Treviso.
As a result, Richards' Exiles team-mate Paul Hodgson was called in to join the training session at Twickenham along with Gloucester number eight Luke Narraway and Bath flanker Michael Lipman.
Aside from the injuries, much of the focus at England's first training session since the World Cup was on Wasps fly-half Danny Cipriani.
The 20-year-old is anxious to learn all he can from training alongside Jonny Wilkinson - but Cipriani also insists he is not in the squad just to make up the numbers.
Cipriani has been learning his rugby at the top end of the European game and is confident he has all the experience required to step up onto the international stage.
"No matter if you are 19 or 35 you have to be the general of the side. Imagine trying to boss Lawrence Dallaglio about - but that is what I have had to do," said Cipriani.
"There are World Cup-winners throughout the side. I have played in some pretty big games and Josh Lewsey said the Heineken Cup final last season was the same intensity as international level.
"Being here and being around all the England players is what I have always thought about - but I still won't feel fulfilled until I get that first cap. And then I will be striving for more.
"It is obviously going to be a massive task to oust Jonny, he has done everything in the game but I am not coming here as number two.
"It is understandable that whenever Jonny has been fit he has started for England because he has done an amazing job.
"Jonny has changed the face of rugby by himself. If I can learn from Jonny that will help me."
Wilkinson has ended speculation over his future by signing a new two-year contract with Newcastle.