Wayne Pivac has accused Scarlets of "probably a lack of respect for the opposition" following their 26-15 Pro12 defeat by Edinburgh.
The head coach said scrum-half Gareth Davies' second-half sending off "made it a lot easier" for Edinburgh.
The New Zealander felt Scarlets had done things "they'd have normally done" in preparation.
But Pivac added: "There's no excuse today - it's probably a lack of respect for the opposition."
Steven Shingler's five penalties gave the hosts a 15-7 lead in the first period.
But with Phil Burleigh and David Denton going over for Edinburgh and Hidalgo-Clyne kicking 16 points, the hosts 15-month Pro12 unbeaten home run was ended.
Scarlets dropped a place to eighth in the table as Edinburgh took over in seventh.
The competition's top six sides automatically qualify for the 2015-16 European Cup.
A seventh slot is also available to Pro12 teams.
That will involve the seventh-placed finisher taking on England's equivalent.
The winners of that game then face a mid-table French opponent for the right to play in next season's European top flight.
Scarlets' fate will be determined in their final four regular season fixtures, three of them away from home.
They travel to Zebre on 11 April, followed by a trip to Newport Gwent Dragons on 25 April.
Cardiff Blues are at Parc y Scarlets on the weekend of 8/9/10 May.
On Saturday, 16 May, the the final round of matches takes place simultaneously with Scarlets at Treviso in their 15:00 BST kick-off.
"It's going to come down to the last week. That's the way it's heading," said Pivac.