Hartlepool let a two goal lead slip at the SMH Group Stadium when Chesterfield came from behind to grab a stoppage time winner through Tom Naylor on a frantic afternoon.
Emmanuel Dieseruvwe had given Hartlepool an early lead before Mancini doubled their advantage within minutes, as Askey’s side looked to continue their early season momentum.
The Spireites hit back through Ryan Coclough before a significant moment for Pools as Mancini pulled up with an injury.
The Frenchman, who has impressed since signing a permanent deal this summer, could be seen clutching at his hamstring and was immediately taken off – the 22-year-old heading straight down the tunnel.
Hartlepool struggled to find a foothold in the game from that point on as Chesterfield levelled things early in the second half through Jamie Grimes before Naylor’s late winner.
But while there will be disappointment in Pools falling to a late defeat, the more concerning aspect longer term this season will be the fitness of Mancini, with Askey suggesting he fears the worst over the midfielder’s injury.
"It’s his hamstring” Askey confirmed to BBC Radio Tees.
"That’s what’s ridiculous about this league is that they play Saturday-Monday. The pace that they play at now at this level far outweighs what it used to be years ago and players are susceptible to it, and when you haven’t got a massive squad then those are the sorts of things that happen.
"It’s less than 48-hours we've had to play again and that’s a consequence of having to do that.”
Askey elaborated on Mancini’s injury: “It looks a long one.
"He’s had a fantastic start to the season and you just hope he’s back sooner rather than later.
"I just feel gutted for him because when you’re in the form he’s in then you just hope it can continue.
"He’s not only a good footballer but he’s a great lad as well, he’s quite infectious for the rest of the players.”
Mancini’s injury means Askey may have to turn to the transfer market to strengthen his squad which is already light in terms of midfield numbers, with Kieran Wallace having also been taken off with a slight injury.
Pools are able to bring players in beyond the close of the EFL’s transfer window and Askey says he will need to look to add to his squad should Mancini be out of action for a prolonged period of time.
"I think you’ll have a hard job replacing him anyway, but it’s an area we’re going to have to have a look at now,” said Askey.
"We’ve got to try and get somebody in quickly.
"You’re always wanting more players in, but the club is where it is.
"We’ve made a fantastic start so there’s no gripes from me. If you’d have said before the game I think everybody would have said the squad looks all right.”