ESSENDON's defensive woes have worsened, with the Bombers now to be without defender Patrick Ambrose for Friday night's clash against Adelaide because of a wrist injury.

Ambrose is set to be booked in for surgery after he fractured the scaphoid bone in his wrist at training on Friday.

Bombers physical performance manager Justin Crow said Ambrose's time on the timelines was yet to be determined.

"Pat Ambrose fell on his outstretched hand during training on Friday. After getting scans today it was revealed that he has a fractured scaphoid in his wrist," Crow told the club's website.

"Pat will have surgery to fix the issue on Tuesday and following the operation we expect to receive further clarification on what recovery time frame is required before he is available to return to play."

Every injury is different, but Carlton's Jarrod Pickett is expected to be sidelined for up to three months after he fractured his scaphoid at training last week.

Ambrose's absence will be sorely felt in the Bombers' backline, particularly with half-back Martin Gleeson (foot) out for an expected four-month period.

Michael Hartley appears to be the most likely replacement for Ambrose, with the defender playing 18 matches last year.

Mitch Brown (adductor) is not yet ready to play, while Aaron Francis returned to the club late last week after a leave of absence but will take some time to be ready to play again.