The Quakers' injury problems have been widely reported in the media and Penney is downbeat about the possibility of players returning in time for Saturday's game with Peterborough.
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"We can't worry about them now, they've been written off the season," he said.
"Julian Joachim won't be available for Saturday, Ryan Valentine won't be, and neither Guy Ndumbu-Nsungu, Neil Austin, Pawel Abbott, Tim Ryan, Andy Oakes. It's getting stupid now.
"The games have caught up with us and the injuries have caught up with us. We have got our backs against the wall now."