MARSEILLE head coach Elie Baup admitted his side's 1-0 Ligue 1 defeat to Nancy on Sunday 'hurts a lot'.
The Ligue 1 giants, who sit third on the table, missed the chance to go level with second-placed Lyon after they also lost on the weekend.
Marseille were poor throughout the match but the complexion of the contest changed when English midfielder Joey Barton was sent off after 61 minutes.
Barton received two yellow cards in the space of five minutes, leading to his dismissal, and visitors Nancy took advantage when they scored thanks to an Andre Ayew own goal on 73 minutes.
A furious Baup was unhappy with the performance and felt Barton's red card triggered the defeat against the second-from-bottom Nancy.
"I'll be careful what I say, but for sure there is a huge frustration...it hurts a lot. It's a way lower performance than we could expect before the game," Baup said.
"We decided on an offensive 4-3-3 formation before this game, something which has been prepared. It was something that we worked on before, but for me the crucial thing was the (Joey) Barton red card.
"Until then we were not brilliant on the pitch, but we were calm, we had some time remaining to score, but after he was sent off it suddenly became much harder.
"We should have got a better result. Nancy played very relaxed because they obviously have nothing to lose."