The 23-year-old has not featured for the promoted Royals this season, with his only gametime coming on international duty with Wales.
Church is out of contract at the Madejski at the end of the campaign and yet to sign a new deal, meaning he could leave on a free transfer in the summer.
A number of Championship sides, including Birmingham, Huddersfield and Ipswich, are thought to be interested in the striker but reports suggest Reading will not allow him to go out on loan until he pens a new contract.
McDermott told the Bracknell Forest Standard: "It's not ideal. We would prefer he signs a contract and then goes out on loan and plays games.
"We will have to see and then reassess it. I need to talk to him and see where we have got to."
He added: "I'm trying to give Simon best advice and I want to make sure all my players do well.
"I think I've done that. I've told him to sign a contract here so he is protected and then get out on loan.
"If he does well then he will come back to us. Or, he does well and gets sold to another Premier League side.
"And if he doesn't do well then he has a three-year contract here at Reading."