Doak is also without Luke Marshall until December as well as scrum-half Ruan Pienaar, Iain Henderson and Dan Touhy.
With the small matter of a European tie against French champions Toulon this weekend and the visit of Newport Gwent Dragons in the GUINNESS PRO12 right around the corner, Doak knows he will have to shuffle his deck.
"Look you lose them at any time of the season and it's pretty tough to take, especially the way Andrew's been playing," Doak told the Irish Times.
"Obviously Luke had a few niggles early on in the season and he was given a run with the Ravens where he picked up another bump, so he's out.
"But hopefully they will get back on the paddock soon. To lose two quality guys like that and obviously the internationals, it puts a bit of a hole in your squad.
"Toulon are a quality side. I don't think there will be any doubt in anyone's mind about the mental state of the Ulster players."
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