The Spaniard has overseen two 0-0 home draws and now a defeat in his first three games in charge - a spell which sees them extend their run of eight matches in the top flight without a victory since beating Tottenham 4-2 back in October.
The loss to Sam Allardyce's side saw the European champions slip even further behind league leaders Manchester United, with the gap increased to 10 points, and Benitez feels that they made it far too easy for their opponents, before admitting that he may have to rush captain John Terry and Frank Lampard back from injury now as a result.
"Normally when you lose, you are not happy — but I was angry," he told reporters. "We did not manage their physical game, the long balls, the second balls, the corners. We gave them too many options to play their game and we could not be comfortable in possession.
"That is when you have to show character and quality — and we did not do that. Character and leadership is always necessary in a team.
"Jose Mourinho's Chelsea team had a lot of character but it is a different time now.
"Terry will train part of the session on Monday so, hopefully, will be close, although with the knee you never know. Frank will train on Monday as well. Sunderland? We will see.
"I will talk with them and then the doctor afterwards. Normally I wouldn't play them if it was not necessary but a lot of players can play with problems. It depends on the risk but character and leadership are necessary in a team."
The 52-year-old believes that the main issue surrounding the team's poor form of late is a lack of confidence, which he attributes to a failure to cope with the physical rigours of the top flight.
|2/1||Chelsea are 2/1 with Bet365 to qualify for the knockout stages of the Champions League|
He added: "We have young players in their first year in the Premier League. They have talent and quality but you still have to show that on the pitch.
"If you cannot cope with the physical demands of the game, you cannot show your quality so we have to give them confidence.
"I've not had too much time in training every day but we will try to adjust things.
"They are experienced players, they've won the Champions League and a lot of trophies but they have to show that character and they need confidence to do that.
"Some players might show character but if one or two are not at that level, the whole team suffers. That is what happened in the second half at West Ham."