The 44-year-old is just seven games into his new role as Schalke coach, his first job since being sacked by Chelsea in November 2012, just six months after winning the Champions League title as caretaker coach.
"There is no time for emotions or sentimentality," said Di Matteo in Monday's press conference at Gelsenkirchen's Veltins Arena.
"Perhaps there will be time for that after the game.
"There will be no feelings of revenge, a win would mean three points, nothing more," added the Swiss-born ex-Italy international.
"In the last two days I have just concentrated on finding the best way of preparing the team," insisted Di Matteo.
He will be up against Jose Mourinho, who has steered the Blues to the top of the Premier League and they are unbeaten in their 12 league games this season, a new club record.
Chelsea are three points clear of second-placed Schalke at the top of the group and the sides played out a 1-1 draw at Stamford Bridge in September, before Di Matteo took charge.
He played for Chelsea from 1996 until 2002, winning the 1997 and 2000 FA Cup titles, and says he had "a wonderful time" at Stamford Bridge.
"I spent many years of my life there, I still have a lot of contact to people there, but we will all just be concentrating on our jobs tomorrow," he added.
Source : AFP