Lilywhites skipper Tom Clarke and Paul Huntington suffered hamstring injuries in the 0-0 draw with Norwich City at Deepdale.
Huntington had to come off at half-time but Clarke stayed on after picking-up his injury in the second half because all three subs had been used.
PNE boss Neil said both had ‘jarred’ hamstrings and hopes neither is too serious.
Clarke had got the nod to start ahead of Ben Davies for the second game running.
It was Davies who replaced Huntington at half-time and slotted comfortably back into the heart of the defence.
Neil said: “Hunts jarred his hamstring and wasn’t able to continue.
“Tom did his hamstring with 25 minutes to go and I think if ever there was a game to epitomise Tom, this was it.
“Even though he had jarred his hamstring Tom was still running down the channels trying to make tackles and rally the boys.
“Tom is a leader of men, people follow him.
“He is a good lad who works really hard and I’m pleased to have him back.”
In terms of Clarke and Huntington being able to play this weekend, there must be some doubt at this stage.
Asked if he expects to have them available for the visit to Bramall Lane, Neil said: “I would like to think so.
“I don’t know the extent of either of the injuries but knowing these two guys, I’m hoping both will be available.”
Saturday’s stalemate with Norwich moved North End a point closer to sixth-placed Millwall but saw them drop back to ninth.
Brentford jumped above them into eighth place and of all the chasing pack have the most favourable remaining games.
Derby, in seventh spot, play their game in hand against Cardiff tomorrow night.
Anything but a win against Sheffield United would end PNE’s play-off hopes.
The Blades, a point behind Neil’s men, are in the same boat.
Even if North End were to win their last two games, they would still need other results to go in their favour.
Neil, though, says his side just have to focus on their own games and go from there.
“We have to take care of our own business,” said Neil.
“Against Norwich we tried to do that but didn’t score when we needed to.
“We go again next week, we have another bite at the cherry so that is a positive we can take out of the situation.
“There are no excuses next Saturday, if we don’t win the game then unfortunately our play-off ambitions will be over for this season.”