Gloucester coach Bryan Redpath has blamed his side's indiscipline for their defeat away to Agen on Friday evening.
The Cherry and Whites lost two men to the sin bin during the second half at the Stade Alfred Armandie as the French side claimed a dramatic late victory in the opening Pool 5 encounter.
"We need to grow up. A few decisions went against us but it was the two yellow cards that killed us," said Redpath.
"We were relatively in control at 13-3 at half time but then poor indiscpline from two senior players has cost us the game.
"When you pay a team with the power and size of Agen, you have to have your full compliment of payers on the pitch at all times. But we spent 20 minutes of the second half down to 14 men. That tells you everything you need tyo know about the game.
"I'm hugely disappointed because we did enough to win but we lost the match, rather than Agen winning it.
"We didn't control the game well enough in the right areas when we were 13-3 up. That's a good score away from home and we were looking comfortable but then poor displine cost us.
"I wouldn't have been that satisfied with a draw because we were looking to win, but I would have accepted it as two points gained away from home."
The West Country side returned home with a valuable bonus point and will be looking to return to winning ways when Italian side Rovigo travel to Kingsholm next weekend.