Stephen Henderson backed Guy Luzon minutes before he was sacked - following the 3-0 home defeat to Brentford.
The Israeli boss was relieved of his duties on Saturday evening (October 24).
The Bees thrashing made it ten winless games for the Addicks and prompted owner Roland Duchatelet to pull the plug on Luzon.
Karel Fraeye has been appointed as interim Head Coach while the board look for a permanent replacement.
Charlton keeper Henderson revealed that his former manager still had the support from the players.
He said: “We’re still 100 per cent behind him.
“I know he’s recently been getting a lot of criticism but he’ll see what’s wrong on Monday and keep going.
“He’s a good manager and a good person - the effort he puts in during the week, that the fans don't see, it’s top notch.
MORE: Charlton appoint Belgian boss as Interim Head Coach
“I know he’ll be hurting more than anyone so it’s not like he doesn't care.
“We’re just in one of those phases where it’s just not happening for us at the moment.”
Charlton had a handful of early opportunities to take the lead but Franck Moussa, Tony Watt and Johann Berg Gudmundsson fluffed their lines.
Henderson, who made his first start of the season after recovering from a long-term shoulder problem, insisted the players should share responsibility for the club’s position.
He said: “Everyone needs to have a look at themselves, me included.
“I’d like to apologise to the fans for that display today - it was not acceptable.
“The crowd were brilliant in the first-half but we let them down in the second - they have a right to be angry because recent performances haven't been good enough.
MORE: Luzon said this about Charlton shortly before being sacked
“I can only say that I’m looking forward to the future as things can’t get much worse from here.”
The former West Ham keeper was helpless to stop Brentford’s three goals and feels that his performances can improve, along with the team’s.
He added: “The Championship is one of the hardest leagues in Europe and we just need to step up.
“When we go to Middlesbrough, we need to show character, no fear and pick up a point minimum.
“Personally I feel good and I know the lads are good enough to get through this rough patch.
“I’m not going to go down without a fight.”
Fraeye, 37, Jose Riga’s former No2 at the Valley, takes his first training session today (October 26).
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