Knight has damaged ligaments in his knee after landing awkwardly following a challenge on Everton's Victor Anichebe at the weekend.
The 30-year-old had been an ever-present this season until he was forced off during the Trotters' 2-0 victory at the Reebok Stadium.
Agony: Bolton defender Knight (right) is set for a spell on the sidelines
'Zat suffered ligament damage. It's not as severe as we first thought but certainly bad enough to keep him out for a period of time.
'There's severe swelling in the area so I think we'll know better in seven to 10 days when that goes down.
'But I think it's fair to say he'll be four to six weeks, which is a terrible loss, first and foremost for Zat, because he's played every game for me since I came to the football club over a year ago.
Early exit: Knight left the field on a stretcher as Bolton beat Everton on Sunday
'He's been outstanding as a player and as a man and the sooner we get him back the better. It is a blow, there's no doubt about it, and we wish him a speedy recovery.'
David Wheater replaced Knight against the Toffees and Coyle added on Bolton's website: 'David Wheater came in for his debut against Wigan a couple of weeks ago and he was outstanding. On Sunday he again looked so accomplished when he stepped into the void following Zat's injury.'
?Davies boost for Bolton as midfielder signs new deal to stay at the Reebok until 2015Bolton 2 Everton 0: Cahill sends a message and Sturridge on hot streakWatch all the Premier League goals every week on our brilliant video playerAll the latest Bolton news, features and opinion
?Explore more:People: Victor Anichebe, David Wheater, Owen Coyle, Zat Knight
Source: Daily Mail
Source: Daily Mail