Southampton boss Ronald Koeman called upon his side to show more fight and greater mental strength in the wake of Saturday's 2-0 home defeat against Tottenham in the Premier League.
First-half goals from Harry Kane and Dele Alli proved enough to secure the points for the visitors at St Mary's Stadium and extend Southampton's winless streak to six games in all competitions.
Kane's opener came amid some poor defending and Koeman felt that that goal summed up why the south-coast side have not managed to win since early November.
"I'm very disappointed," he told Sky Sports.
"If you look back at the first goal from Kane, it is incredible how we were so defensively naive in that situation.
"It was three defenders against one attacker and still the one attacker was given the chance to go one-on-one with the goalkeeper.
"Everybody at the club needs to understand that we are in a difficult situation and we have to change our mentality.
"We know we can play good football, but with our position in the table at the moment, you need something different.
"You need to win every battle on the pitch and we are losing too many of those battles, as we did for that first goal.
"We have to have the right mentality and if we don't have that, we are going to have many problems in the Premier League from now on."
Southampton's strikers did not escape the Dutchman's criticism either after they failed to capitalise upon a number of decent chances, notably during an opening quarter in which the hosts were much the better side.
"That was the difference today," he said.
"They had more of a killer mentality than we showed both defensively and also attacking-wise.
"We had the best chances in the game, but they were more clinical and had more quality.
"We started well and were the better side, but again today, we have committed terrible mistakes and haven't shown that killer mentality."
Southampton remain in 12th place despite the defeat, but face another stern test in their next outing, which sees them entertain second-placed Arsenal on Boxing Day.
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