Van der Mark was training for the new WSBK season last weekend when he fell off his mountain bike in an accident, breaking his leg and requiring medical treatment.
The Dutch rider has already been forced to miss this week’s pre-season test at Misano and is not expected to recover fully until the second round of the year later next month at Assen, his home event.
“It’s a real shame at the last minute that Michael took an injury out training,” said Muir. “Nothing sinister, it was a very unlucky situation on a mountain bike. It’s happened, we must wait for the prognosis for that.
“We should find out soon how long it’ll take for the recovery and when he can have an operation, but for sure it’ll need to be plated. We’ll wait for the answer for that.
“His spirits are down, just disappointed because we worked so hard over winter to prepare the bike. When he has a target, when we have an understanding.
“Our honest opinion is it will be more like Assen for the…