Problems in both full-back positions mounted up before and during the 3-0 derby defeat to Blackburn Rovers.
Joe Rafferty’s red card in the Rovers game will see him suspended at Vicarage Road.
He will serve a one-match ban – the punishment for a sending-off for a foul which denies a goalscoring opportunity.
Another costly card in Tuesday night’s game was the yellow shown to Alan Browne.
That was the skipper’s fifth booking of the season and triggers a one-game ban.
Although a midfielder by trade, Browne has been used at right-back occasionally.
North End are awaiting a decision from the FA on the disciplinary charge levelled at Darnell Fisher in the wake of the Sheffield Wednesday game last Saturday.
Fisher was seen to grab the genital area of Wednesday’s Callum Paterson while they waited for a corner to be taken.
The charge which the FA have made is the one which covers violent conduct and can carry a three-game ban.
PNE made an initial response to the charge by 6pm on Tuesday as requested and the case is ongoing.
Josh Earl was missing from the squad against Blackburn, having been on the bench for the previous three games.
Fellow left-back Andrew Hughes has been out of action since the end of October with a torn hamstring.
On Tuesday night, Lewis Coulton was called up from the youth team to be on the bench as left-back cover.
Coulton was joined among the subs by another second-year scholar Jacob Holland-Wilkinson.
Neil said: “I wouldn’t call it a shortage, we might literally not have any full-backs available for Saturday.
“It is something we will have to get on with.”
One way around it would be a change of system to 3-5-2, allowing wingers to operate in the wing-back slots.
Whichever formation Neil goes with and who he has available, he will need a huge improvement from his side against Watford.
The defeat to Blackburn provoked an angry response from the fans – the manner of the loss especially.
Neil admitted he chose a direct approach rather than playing out from the back.
“We are not at the stage where we can work it out from the back, we don’t have that type of player,” said Neil.
“We needed to be more direct in our play, pick up second balls and play more in their half where we can risk it a bit more. We knew Blackburn would dominate the ball. Did I want that? Not really but sometimes you don’t have a choice.”
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