Onions sustained the injury in the nets ahead of the first Test in Chittagong
England and Durham seamer Graham Onions is likely to miss the start of the new season after scans revealed his back injury is worse than initially feared.
The 27-year-old left England's tour of Bangladesh early with the injury and he will now miss next month's World Twenty20 tournament in the West Indies.
Onions will also miss Durham's game against the MCC in Abu Dhabi next week.
"He may be out for a month or two and probably won't make the start of the season," said Durham coach Geoff Cook.
Onions had been hopeful of recovering from the injury in time to join his county champion team-mates in the Middle East for the traditional curtain-raiser to the domestic season against the MCC.
However, X-rays revealed the injury, which he picked up in the nets in Chittagong, is more serious than first thought and he has gone for more scans.
"We have not been able to identify the exact cause of the problem," Cook told the Northern Echo.
"He had another scan over the weekend, and we are waiting for the results.
"It is disappointing he probably won't be fit for the start of the season - especially because he has international aspirations."
Onions is among England's 30-man provisional squad for the World Twenty20, which is set to be halved before next week's deadline.
He has taken 28 wickets in eight Tests since making his debut against West Indies in 2009.
Durham are bidding to become the first side since Yorkshire in the 1960s to win three successive county championships titles.
They host Essex at The Riverside in their opening game which starts on Thursday, 15 April.
The four-day match against the MCC, which is usually played at Lord's, is being staged in the United Arab Emirates and pink balls will be used.
A Durham spokesman told BBC Sport that Cook was unavailable for further comment.