Inter Milan manager Frank de Boer blamed his players for starting their Europa League clash with "the wrong attitude" as they slumped to a 3-1 defeat to Sparta Prague on Thursday.
Despite finding their form in Serie A, the Nerazzurri have begun Group K back-to-back defeats Hapoel Be'er-Sheva and Sparta Prague.
And De Boer suggested after the game that the players did not approach their trip to the Czech Republich with the correct mentality.
"If you start with the wrong attitude, you can talk about tactics all you like, but the first thing is to have the right mentality," the manager told Sky Sport Italia.
"On the second goal we gifted an incredible opportunity. It's not possible to concede a goal like that. In the second half we did slightly better, but certainly not playing the way I want to see Inter play. After the red card it all became more difficult and the 3-1 sealed it.
"We gave the ball away too many times and must improve a great deal in that sense, because otherwise it's going to be difficult over the next few games too."
Despite some squad rotation between Serie A and the Europa League, De Boer said he expects all his players to approach the game positively.
"Assane Gnoukouri could play on Sunday as well, but hadn't played for months, so needed some time on the field to find his form," De Boer said.
"Antonio Candreva has been ever-present and we only changed a couple of players, like Mauro Icardi and Ivan Perisic. The problem is whoever steps on to the pitch must have the right spirit."
Felipe Melo agreed with his manager, saying his team did not stat playing until the score was already 2-0 in favour of their opponents.
"We must understand that Europe is not simple, it is different to playing in Italy. We have to play every game as if it's a derby and so far we haven't done that," Melo said.
"The second half was better, but after the red card it became really tough. Before the break we only started playing once we were already 2-0 down.
"We expected Sparta Prague to be strong, because they changed Coach and that always creates an extra desire to prove yourself within the squad.
"This is not the moment to talk, we need to bring out everything we've got and prepare for Roma, because there's no time for anything else.
"On the second goal we should've closed down the free kick, I was taught that as a child, but today nobody put themselves in that position and we left the opponent clear. It's a collective error and everyone is to blame when we lose, just as everyone deserves credit when we win."