"Jonny has suffered a pretty significant knee injury that requires surgery," the club's head coach David Humphreys told the Gloucester Citizen.
"He's seeing a specialist on Tuesday and based on the outcome of that we will have a much clearer picture of what needs to be done."
May, one of the fastest players in the game, became a regular under Stuart Lancaster and started all of England's World Cup games.
He was likely to retain his berth under new coach Eddie Jones but now faces a long spell on the sidelines after sustaining the injury during Gloucester's 39-39 draw with Harlequins at Twickenham on Dec. 27.
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England start their Six Nations campaign away to Scotland on Feb. 6 and visit Italy the following weekend.
(Editing by Amlan Chakraborty)
