The referee is usually only seen on court during the administration of a medical timeout.

After going up by 4-1, he took a medical timeout and had his trainer massage his legs.

After the medical timeout, Hewitt dropped the third set and was overrun in the fourth.

The first of which occurred at 1-3 in the second set, a fall that saw Li incur a 10-minute medical timeout.

That's when Djokovic, hobbled with a back strain, took a medical timeout while leading at 1-0.

At 3-3 in the first set, Clijsters rolled her ankle and required a medical timeout.

But after a medical timeout, Avants returned to her animated self.

After a medical timeout and holding serve to force a tiebreak, rain forced play to be suspended for nearly two hours.

There were no indications anything was wrong with Djokovic until he called for a 10-minute medical timeout when he fell behind in the third set.

Djokovic's medical timeout - three games into the third set - did little to help him.