The Belgian defender will now miss next week's trip to Birmingham after being shown a straight red by referee Martin Atkinson for what the West Yorkshire official deemed denying a goalscoring opportunity when tussling with Guillermo Franco as they chased a long ball into the Arsenal box.
Goalkeeper Almunia, 32, produced a stunning save from Alessandro Diamanti's resulting penalty to prevent what would have been an equaliser, and that changed the balance of the match.
With William Gallas still hampered by a calf problem which has sidelined him for the past seven matches, Wenger admits he has little option but to call on both Campbell, the 35-year-old former skipper who rejoined Arsenal in January, and fellow veteran Mikael Silvestre, 32, to once again step into the breach.
The Arsenal manager, though, has every faith the senior men in what is a young squad can deliver.
"I hope missing Vermaelen at Birmingham won't be a problem - but we cannot continue to lose centre-backs, that is for sure," Wenger said.
"You also cannot have six centre-backs at a football club because that doesn't make sense.
"Sol Campbell was outstanding, but to repeat the games could become a problem for him so I think I have to give him a big holiday next week to recover.
"He is very important to us and I think it was a very good signing.
"Everybody said I didn't sign anybody and now you can see that I signed somebody.
"His experience is vital in the dressing room, and you need it especially when we get to the period we are in.
"It is important you have players like Silvestre, Sol Campbell and Almunia, who are very influential. They have done it before so players listen to them."
Arsenal had taken an early lead through Denilson, and regrouped for the second half when midfielder Alex Song dropped back into the centre of defence alongside Campbell.
"Song was absolutely outstanding. It looked so easy for him to play in this position," Wenger declared.
"I know he can play there, but he was outstanding in midfield earlier in the game. I have no fear to continue with him at centre-back if needed."
There is now little to chose between the top three. Arsenal would appear to have the easier run-in, as United and Chelsea meet at Old Trafford over Easter, but Wenger maintains there is no margin for error in their remaining seven matches.
"It will be exciting now until the end, we have three teams in the fight, so let's see," he said.
"There is no room for error - the only target is to win the next game and give absolutely everything. That is what we will go for."
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