Defender Kyle Walker limped off with ankle ligament damage against Newcastle and skipper Chris Morgan received his fifth booking of the season, meaning he too will miss the clash with his former club at Oakwell next Monday.
Blackwell said: "We lost (Andrew) Taylor in the first 20 minutes against Cardiff, so that was another one we lost and we had to rearrange again, then we lose Kyle Walker and we have to rearrange again and now we've lost Morgan.
"I've never known a season like it. There will be something like 14 players on the sidelines out of a squad of 25 and that just tells you how stretched we are.
"We are very stretched at the moment. We just need to have a bit of luck. I don't think there's anything else wrong."