The England paceman missed most of last season after surgery in America and inflammation of the joint has continued to plague the 28-year-old this term.

Jones will miss the Championship game with Essex on Wednesday but could play the weekend's Friends Provident Trophy match with Hampshire at Swansea.

The bowler has managed just 37 overs in the Championship so far this season.

Glamorgan captain David Hemp said: "It's very frustrating for Simon because his knee keeps swelling up."

Jones played no part in Monday's three-wicket loss to Surrey in the Friends Provident Trophy at Cresselly, in a match that saw his county's bowling resources stretched to the limit.

As well as Jones, former skipper Robert Croft and Andrew Davies were both missing, while Damien Wright pulled up after four balls and teenager James Harris was absent taking exams.

"I feel sorry for Simon, as he is resting his knee and doing everything he is told," Hemp added.

"He is taking 10 days off or a week off after a game as stipulated by the ECB (England and Wales Cricket Board), but to come back after that with the knee still swollen is very disappointing.

"Simon gets treated by us and he is in constant consultation with the ECB physios, but the fact that it's swollen up again after a period of rest is a bit concerning and he's gone back up to talk to them."

Wright injured a thigh muscle during Monday's one-day match at Cresselly, and faces a spell of two to four weeks on the sidelines.

Spinner Croft, who sustained a calf strain last week at Swansea, is again doubtful and will have a late fitness test to see if he will figure against Essex.

Glamorgan call up Michael O'Shea, Nicky Peng and Gareth Rees for their first Championship appearances of the summer, while Harris is also available following his AS-level exams.