Di Matteo has transformed Chelsea's season since taking over as caretaker manager after Andre Villas-Boas was sacked in March, but there is no guarantee he will be offered the job permanently even if Chelsea are crowned European champions for the first time.
Although Chelsea won the FA Cup earlier this month and are now within 90 minutes of what would be their greatest triumph, the signals emanating from Stamford Bridge indicate that the club's billionaire owner Roman Abramovich wants a more glitzy, bigger name to fill the role.
Heynckes, 67, one of Europe's most experienced and successful coaches, who would become only the fourth man to guide two clubs to European Cup success, thinks letting Di Matteo go would be a mistake.
"I think the position of Chelsea and Di Matteo can be understood. Chelsea are a huge club, a top club in Europe, and you will try to find the best possible coach, someone who has already won something and already brought titles and has all the attributes you need for this kind of job," he said.
"But Di Matteo makes an excellent impression on me and if I was Abramovich, I would continue with this young man.
"He led Chelsea to the final with a calm head, and step by step he established contact with the players. I think really, until today, his work has been outstanding and no matter if they win or not, I hope he stays there because there is a need for continuity."
Heynckes thought there were differences between his departure from Real in 1998 and the situation Di Matteo is now in, saying he knew from the previous December he was going to be sacked and would have left anyway.
Di Matteo's position has been strengthened since he began to breathe new life into Chelsea's season after Villas-Boas's departure, and all he has said in response to hundreds of questions about his future is: "lets wait and see."
Although Chelsea finished sixth in the Premier League, their lowest position for a decade, and will miss out on the Champions League next season if they lose on Saturday, he has certainly restored their pride and self-belief.
They have lost only three times in 20 matches in all competitions since Di Matteo took over and he gained widespread respect for masterminding their semi-final victory over Barcelona.
For that alone, besides being a former Chelsea player, many fans believe Abramovich should at least give him a chance in the role permanently. Clearly, so does Heynckes.