Adams' side have kept three clean sheets in their seven matches
Port Vale manager Micky Adams has admitted that he is concerned with the lack of defensive cover in his squad.
Lee Collins, John McCombe and Gareth Owen have started every game for the Valiants as part of a three-man backline this season.
"That's an area that slightly concerns me. If we lose one of those, and if it does we'll have to look at changing the system," Adams told BBC Radio Stoke.
"The three in the team are the only three that we've got at the club."
Adams has revealed that veteran striker Geoff Horsfield will play in defence for Vale's reserve side against Macclesfield on Wednesday.
Meanwhile, the Vale boss has been happy with the form of Bristol Rovers loanee Lewis Haldane, who has made two appearances from the bench since moving to Vale Park for a month on 1 September.
"He offers a genuine threat and his impact as a substitute has been good," added Adams.
"He'll be itching to start a game, and by the end of his month with us I expect him to have started a couple."
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