The spinner reportedly suffered the problem while playing five-a-side football and is not expected to return until next season
Worcestershire spinner Ben Twohig will miss the whole of the 2019 season with a serious knee injury.
The 20-year-old suffered an anterior cruciate ligament tear while playing five-a-side football, according to Cricinfo.
Twohig will undergo surgery next week before starting a period of rehab which is expected to last between six and nine months.
Head of sports science and medicine Ben Davies said: “Ben Twohig had an MRI scan last week which confirmed a diagnosis of an anterior cruciate ligament tear.
“He is due to have surgery on April 16, an arthroscopic procedure, and will then follow rehab for the next six to nine months.
“Ben will undergo the rehab programme with a view to hopefully taking part in pre-season next year for the 2020 season and hitting the ground running.
Chief-executive Matt Rawnsley added: "Obviously, for Ben to get this injury is extremely disappointing for him and the club.
“Our medical team is committed to the rehab stage and will endeavour to get him back fit again as soon as possible.”
The Yorkshire-born player enjoyed his breakthrough season in 2018, making seven County Championship appearances and taking 10 wickets.