The 32-year-old underwent a scan on Wednesday and was ruled out of Saturday's match at Northampton Saints.
"We have got a scan being done on him having realised he is not quite right," John Kingston, Harlequins director of rugby, told reporters on Wednesday.
"He has been away with England for two or three days and they have done some treatment on it. He is not fit to play this weekend.
"It's clearly something that's not quite right and therefore, after he's re-aggravated it, it's better to leave it a bit and give it some more time."
Although coach Eddie Jones recently suggested Anthony Watson or Elliot Daly could fill in at the fullback position, Kingston backs Brown to play a pivotal role heading into the 2019 World Cup in Japan.
"Mike Brown is the first-choice fullback for England in my book and people will always say 'who are the competitors?' -- that is the nature of the business," Kingston added.
"He wants to play well for England, he wants to be involved in the World Cup -- and there's no reason he can't be. It would be a big mistake to write him off."
Brown has 62 caps and has started all but one of England's matches under Eddie Jones.
England host Argentina at Twickenham on Nov. 11 before playing Australia and Samoa at the same venue over the next two weeks.
(Reporting by Hardik Vyas in Bengaluru)
