Chris Tremlett and Graeme Swann are doubts for England

Swann is a doubt for the first Test against Pakistan (GETTY IMAGES)

Chris Tremlett and Graeme Swann's fitness remains in doubt for England's final warm-up match against a Pakistan Cricket Board XI tomorrow.

As Tim Bresnan flew home from the United Arab Emirates this morning because of post-operative pain in his bowling elbow, Tremlett's eye infection and Swann's sore thigh were still keeping England's medical staff busy.

Tremlett had to miss the opening victory, at the start of this Test and limited-overs tour against Pakistan, and Swann was unable to bowl or field on the final day.

A scan on Swann's injury niggle has yet to take place, and Tremlett's eye has so far failed to respond to treatment.

England have other issues to settle in terms of appropriate preparation for all, in the three-day match against the PCB at the GCA ground, before the first of three Tests on January 17.

The uncertainty, particularly over Tremlett, opens up the possibility of a heartening return to England colours for Graham Onions.

The Durham seamer has not played for his country since the new year Test in Cape Town in 2010 - in which he helped to salvage a dramatic last-ditch draw by blocking out the final over, for the second time in that series.

Onions subsequently suffered a career-threatening back injury, and a long road back after surgery, but was named as cover for England here and - following Bresnan's injury - finds himself possibly on the verge of a comeback.

The 29-year-old had inevitable mixed feelings, at the opportunity which has come his way because of a fellow pace bowler's misfortune.

"I feel really bad for Tim," he said.

"He has been an integral part of England's side for the last year or two.

"Whether or not he was expecting it, I don't know. But he hadn't done any bowling, and that's probably the reason why I was out here because there were certain injury doubts over him.

"It's up to me now to try to come into the squad and try and make a difference."

PA