Richards was forced to use looseheads Sam Lockwood and Sami Mavinga at tighthead in the 31-13 loss after having lost regular tightheads Logovi’i Mulipola, Trevor Davison and David Wilson to injury during the week.
The Falcons boss asked EPCR for special dispenstion to draft in a replacement tighthead, but the request was rejected, leading a furious Richards to accuse the the Champions Cup organisers of showing a flagrant disregard for player welfare.
Newcastle’s director of rugby said: “You lose three tighthead props in 24 hours, you ask for dispensation to bring in another one and you’re not allowed that so you have to play a loosehead on the tight.
“It’s not like playing a left wing on the right wing or an inside centre at outside centre. There is a safety issue there and they weren’t prepared to address it so I was particularly disappointed with it.”
Richards said he had spoken with Edinburgh counterpart Richard Cockerill about his concerns before the game, which he later described as an ‘unfair contest’.
“In the Premiership, you have the ability to register somebody say for a Saturday game up to midday on Friday,” Richards told BBC Sport.
“In Europe you’ve got this issue whereby on a Tuesday at midday I passed that point, you’re not allowed to change anybody.
“I spoke to Richard on a couple of occasions, he would much have preferred us to have put a tighthead in there.
“I just thought at certain times in the game it made it a bit of an unfair contest.”
Richards was proud of the character shown by his second-string side, who led at the interval but were run off their feet when the hosts upped the tempo in the second stanza.
“It was always going to be a difficult second half,” he said. “We created a lot of opportunities and didn’t take them – we will look to nail them next week.
“For the integrity of the game and the competition the boys said ‘Look we’ll give it a go’, and to be fair to them they stuck at it.”