Essex spinner Tim Phillips faces up to six weeks out after undergoing knee surgery.
The left-armer, 27, sustained the injury while playing in the recent second XI fixture against Surrey.
"Tim underwent surgery yesterday to repair damaged cartilage in his right knee," said Essex physio Mark Thomas on Thursday.
"The surgery went well and he is expected to return to play in six weeks."
Phillips featured in his county's opening FP Trophy match of the season against Kent but is now unlikely to challenge for a return until around the start of the Twenty20 Cup in mid-June.