Essex have confirmed Australian Test fast bowler Peter Siddle will now not be joining the county for this year's T20 competition.
Siddle left Australia's current tour of the West Indies early after complaining of lower back soreness.
He has now been told he needs a month's rest followed by rehabilitation.
Essex head coach Paul Grayson said: "We understand when we sign any overseas player there is a risk of an injury on international duty."
The 27-year-old pace bowler has taken 114 wickets in 31 Test appearances at an average of 29.03.
Grayson said Essex will look to recruit another overseas player for the T20 competition, but Essex chief executive David East said availability could be a problem.
"We only found out overnight and we're putting our heads together about who would suit the balance of the squad and who is available, that's the biggest difficulty," said East.
"We were all looking forward to Peter joining us, but obviously no-one can do anything about an injury."