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 comeback. This will be the target for me. There’s no replacement at the moment, we’ll discuss it with BMW.”
In the absence of van der Mark, new signing Scott Redding has been single-handedly completing BMW’s test programme at Misano, setting the 10th quickest time on the opening day of the running - a 1m35.592s.
This was over 1.5s slower than the benchmark set by Alvaro Bautista, who has returned to Ducati this year after a two-year stint at Honda.
Satellite BMW team Bonovo MGM enjoyed a better showing than the factory squad, with Loris Baz ending up fourth and Eugene Laverty classified eighth on the sister M1000RR.
BMW is heading into the 2022 season on the back of its first comeback victory in WSBK after van der Mark triumphed in a wet-weather race at Portimao in October.
The German manufacturer has been boosted by the addition of former Ducati rider Redding, who finished runner-up to Kawasaki’s Jonathan Rea in his first year in WSBK in 2020 before slipping to a still-respectable third in the championship last year.
