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Richard Cockerill refused to use the absence of a host of players through injury and international calls as an excuse for Leicester's shock defeat at Kingston Park.
With around 18 players ruled out, the Tigers went down 26-14 to a determined Newcastle side battling to claw their way out of the relegation mire.
"I'm not interested in how many players we had missing," said the Tigers director of rugby, who also saw his side lose 10-3 to Sale last week.
"We are able to put out a decent side and there's simply no excuse. We knew Newcastle would come at us and our lack of composure and control on the ball was obvious.
"We're pretending if we think that that's an okay result and that's not taking anything away from Newcastle.
"That result will cost us in the shake-up at the end of the season. Next week is now a huge game on the back of two losses."
Leicester were 20-9 down at the break after two converted Newcastle tries and two penalties from Andy Goode.
They were also on the wrong end of the penalty count.
"We got exactly what we deserved which was nothing," said Cockerill.
"We were beaten at every contact point and, clearly, Newcastle wanted it more than us. We were beaten across the board. There's no getting away from it and I'm bitterly disappointed, it's just not acceptable.
"We need to take a good hard look at ourselves and put things right and do it quickly."
Newcastle produced their best display of the season, scoring tries through Simon Hammersley and Adam Powell, both converted by Goode, who also kicked three penalties. Craig Willis added Newcastle's final penalty in the 80th minute.
Freddie Burns kicked three penalties for Leicester with Laurence Pearce scoring the solitary Tigers try 15 minutes from time.
Falcons director of rugby Dean Richards said: "I told the lads at half-time they just had to go out there and lay their bodies on the line again, and they did.
"The pack were outstanding and Sean Robinson and Will Welch were outstanding in an outstanding pack.
"There is now a sense of belief among the players and this team is in a good place. We had a difficult start to the season with lots of injuries - we still have lots of players sidelined but the players now have confidence in each other and that makes it easier to play."