Almunia - who missed the first leg through injury - was sidelined by a chest infection earlier in the campaign, which followed a family bereavement.
The Spaniard, though, has returned to help bolster the Gunners' bid for both Barclays Premier League and Champions League glory.
"I had a difficult start to the season, but after a few games I came back stronger and now I am in a very good position to help my team and look forward to the rest of the season because we have chances to do things," he said.
"When my mother-in-law died during pre-season, the manager let me go to Spain and stay with my family, to spend all the time I wanted.
"She was a very special person for me and my wife. She was great.
"It is difficult, but when you are mature it is a bit easier to cope with things. It all depends on the sensitivity of the person.
"Things can affect you as much as your head lets it - when something really bad happens to you, you never know how your mind will react.
"At that time, I was very low, not very strong to continue, but I took my time and now I am ready again."
Almunia added: "Every person, every player has had experiences, where the next day you have to wake up and continue working, getting on with your life.
"This squad is very young, and if anybody needs help, I am here for them.
"My role will be the same as when I am not captain and just in goal - I have the personality, and will help the team as I do normally every game. The armband does not change anything in myself."
Gunners boss Wenger admits the loss of Fabregas is a big blow, but maintains his team have enough quality to still progress.
And Almunia hailed the influence of his young compatriot.
"Cesc is the spirit of this team - he is our captain, he is a fantastic player and every time he is not on the pitch we miss him a lot," said the Arsenal keeper.
"But all the players are convinced and 100% committed to get through."
Denmark forward Nicklas Bendtner missed a string of chances in the 3-1 Premier League win over Burnley on Saturday.
Almunia revealed the 22-year-old had been on the receiving end of some light-hearted banter from his team-mates.
"Nick is a special guy. He is young and he is learning," he said.
"I think he needs people around him who tell him the truth all the time.
"When he does well, of course everybody will tell him he is good - but when he misses goals he needs someone to push him to improve. That is what we try."
Almunia added: "I hope he reacts tomorrow and I think he is encouraged by the chances he missed in the game against Burnley. Today he has been training very well."