Established Test gloveman Prior was dropped from the side during the team's 5-0 Ashes thrashing in Australia but it had been expected the 32-year-old would force his way back into the team for next month's two-Test series.
However, the 32-year-old Sussex stumper has since suffered an Achilles injury which has restricted him to just two first-class matches this season, both at the start of April.
It had been hoped Prior would return for Sussex's First Division County Championship match away to Middlesex at Northwood but rain caused the fixture to be a washout.
Even before no play was possible on Thursday's final day it was decided Prior would be better off undergoing a training session with England wicketkeeping coach Bruce French.
Afterwards, Prior told his Twitter followers: "Hard session with frenchy today, as always, and so far the injury has responded very well!
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Prior is now set to return to Sussex duty in Friday's Twenty20 match away to Glamorgan, although it is possible he