Blackwell's squad this season has been struck down by constant injury problems and as United's play-off ambitions fall by the wayside, the manager is in no doubt as to what has caused the slip down the table.
"It started badly with Ched going off with a broken collarbone, and then Ward went off with a hamstring and also Williamson with a hamstring," Blackwell said.
"It's never easy at the best of times. That is seven or eight players out with injuries in a squad of 21, 22, so you can see why we have got a problem.
"It has been like that twice this season. I said for the run-in that we could not afford injuries or suspension but we have got them by the bucketload now."
Despite seven consecutive away defeats, the Blades remain just four points outside of the top six, but Blackwell was subjected to some angry chants by the United faithful at full-time, who were demanding his dismissal.
"Last season we broke the club record (for away wins) and this season we couldn't win a raffle," he acknowledged.
"We are always in games, but we weren't smart enough and we couldn't create enough.
"It is frustrating. If I could get my team out, the team I want, I think we would have a chance, but I can't get it out.
"These fans also know the problems at the football club. I have had 24 new signings in a season. You don't have to be a genius to know you can't carry on doing that. So to be where we are is a phenomenal achievement, but it has been one of those seasons where we have lost the parachute payments."
Peterborough boss Jim Gannon has ruled out any hope of his side being able to avoid an instant return back to League One.
Despite the three points, Posh remain 11 adrift of safety and Gannon will not go back on his assessment after Saturday's defeat to Coventry that his side are not good enough to stay up.
"I think it was important to be brutally honest. I wasn't playing any reverse psychology on Saturday," he said.
"When I came to the club we had three wins out of 28 and we needed to win nine out of 18 and it was an incredible task to ask of the players.
"I genuinely feel we won't pick up the results we need but all I want us to do is show fighting spirit."
Source: Team Talk
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