Yorkshire suffered an injury scare on the second day of the Roses match against Lancashire when bowler Ryan Sidebottom was forced to leave the field with a hamstring problem.
The 36-year-old left-arm paceman was unable to bowl after lunch in the County Championship Division One match, although Yorkshire coach Jason Gillespie is hopeful the problem is not too serious.
"He's just felt something at the bottom of his hamstring, so it will be an ongoing assessment of that," said the former Australia fast bowler.
"We will make a decision on whether we need to get him scanned, and we'll probably know more tomorrow and make a plan from there.
"At this stage, it looks like a little tweak, and we don't think it's serious - but we've got to look after him.
"He bowled a couple of balls at lunchtime but he was feeling it a little bit.
"With 'Siddy' being such an important member of our squad, the leader of our attack, we want to make sure he's 100 per cent."
Lancashire were bowled out for 325 with Jack Brooks taking five wickets and Liam Plunkett claiming four victims, while Tim Bresnan took only one wicket despite getting through 27 overs.
Gillespie, whose side closed on 29-0 in reply, was encouraged that the Yorkshire attack performed better at their second attempt than they had in the one session possible because of rain on day one at Headingley.
"It was an improvement on yesterday, because we didn't bowl well then," he said.
"The lads put their hands up and said they could do better. I still think we can bowl better than that, but it was an improvement.
"If we bowl to our potential I think we could have restricted them a bit more. But we've started well with the bat; it's a good pitch - and we're looking forward to putting a good score on the board."