Harlequins have confirmed that full-back Brown, 34, will undergo surgery this week to address a knee injury sustained at the end of preseason.
Mike Lancaster, Head of Medical Services at Harlequins said: “Mike has been the model professional and is fully committed to a conservative reload and return to play, within hopefully six to nine months. Unfortunately, after playing the last two games, the restriction in function would not allow Mike to perform at his best or indeed allow optimal preparation within the week.
Head of Rugby Paul Gustard added: “Losing Mike is a big loss to the squad. He has tried hard to train and play over the last few weeks but unfortunately his situation has worsened, and it would be damaging to his long-term knee health if he continued to try and play.
“He is of course disappointed, as ultimately Mike wants to compete and give his all to the shirt. Under the guidance of our outstanding medical team led by Mike Lancaster, allied to Browny’s incredible attitude to improve and his diligence to rehab, I know he will do everything he can to return to play faster than anticipated.
“We will look to see how we can use Mike in other capacities to help the squad.”
Welsh hooker Scott Baldwin, who joined the Club in the summer, also sustained an injury to his neck in the side’s Champions Cup fixture against ASM Clermont Auvergne.
Mike Lancaster confirmed: “Scott will undergo surgery next week to address his neck injury. He is understandably disappointed to be missing out on game time, but his professionalism and focus will no doubt help in expediting his return to play in the new year.”
Gustard continued: “Scott has settled in really well and is a popular member of the squad. He was outstanding in pre-season and demonstrated strong leadership qualities, which will prove to be an asset to the Club moving forward.
“He had made a promising start to the season and his injury is further loss to a position where Rob Buchanan is yet to regain fitness and Max Crumpton is out until the new year.
“We know Scott is determined to attack his rehabilitation the same way he does a scrum and he will do all that’s required to return to play faster than anticipated. I know our fans will wish him the very best in his recovery from his forthcoming surgery.”