Pakistan remain hopeful Yasir Shah will be fit for the opening Test with England on Tuesday despite a back spasm during a training session in the United Arab Emirates.

Leg spinner Shah comes into the series as one of the most dangerous bowlers in world cricket, having taken 61 wickets in his 10 Tests.

During a net session on Monday the 29-year-old bent down to stop a ball hit back at him, but then fell in a crumpled heap and subsequently left the session in discomfort.

Captain Misbah-ul-Haq confirmed Yasir's back would be monitored over the next 24 hours, before a decision is made on whether he will start the match in Abu Dhabi.

Meanwhile, opposing skipper Alastair Cook knows Yasir's absence could be a big boost for England.

"You never know with these things, of course it'd be a loss for them," he said. 

"Clearly he's a fantastic bowler who not many of us have faced in Tests."