Pardew hits out at Chelsea owner
Di Matteo was dumped as Chelsea manager after the 3-0 Champions League defeat to Juventus on Tuesday.
Abramovich is now looking for the London club's ninth manager in nine years, with Chelsea's passage through to the knock-out stages no longer in their own hands.
Pardew was in disbelief about the sacking and believed football fans would feel the same way.
"Astonished really. It just goes to show you how precarious we are as Premier League managers and you can't take anything for granted," Pardew said.
"The shock that should be there from the fans and the media should sound something to the owner of that football club (Roman Abramovich).
"I don't know if that's their ninth manager or whatever it is in so many short years, it's just not fair."
Pardew stood by Di Matteo and believes the club should have too, citing the Italian's Champions League and FA Cup victories last season.
"As far as I'm concerned he (Roberto Di Matteo) has done absolutely nothing wrong. The philosophy was to change the look of the team which he's tried to do and he's won two competitions in less than a year, so it's unbelievable," he said.
Meanwhile, Pardew said midfielder Yohan Cabaye requires surgery on a groin injury sustained against West Ham on November 11.
The 26-year-old limped off at the end of the clash and subsequently missed the 2-1 home defeat to Swansea on Saturday.
And Pardew is rueing the loss of the France international as his side bid to overcome their sluggish start to the Premier League season.
"(Cabaye) will definitely have an operation, and we think it's going to be on Friday or Monday, I'm not sure. That's a blow to us because he's a top player for us," he told reporters.
Pardew also expressed concern over Shola Ameobi's fitness ahead of Thursday's Europa League clash with Maritimo.
He added: "The only one we are a little bit concerned about is Shola. He's got a slight groin niggle, so we are going to have to see how he shapes up for Thursday's game."