The former boss won a Champions League and FA Cup double after less than a season in charge, but was dumped by club owner Roman Abramovich, after defeat to Juventus which left Chelsea on the verge of an early European exit.
But Mata - who has now played under three managers at Stamford Bridge in less than two seasons - feels the 42-year-old will be back in the game before too long as because he is a popular person.
"Roberto [Di Matteo] won two trophies in just nine months which is very difficult to do, so you have to recognise the job he did," he told reporters. "But he has been sacked — that's how hard and unjust football is.
"Just six months ago we were celebrating having won the Champions League."
|5/1||Juan Mata is 5/1 to score the first goal when Chelsea take on Fulham with William Hill|
And while Di Matteo may currently be out of a job, the Spanish midfielder believes it is only a matter of time before another club picks up a young manager with such impressive recent successes on his CV.
He continued: "He's a very good coach and a legend at Chelsea, people have such a lot of affection for him.
"There were hard and difficult moments, as there can be at any club, but they were more than made up for.
"And I'm sure he'll soon have the opportunity to coach again."