The Catalan club suffered two consecutive defeats - 1-0 at Chelsea and 2-1 at home to Real Madrid - before the Blues knocked it out of the Champions League at the semifinal stage on Tuesday.
The former Blaugrana midfielder will manage the Camp Nou side’s final few matches of the 2011-12 campaign before handing over the reins at the end of the season to assistant Tito Vilanova, and Di Matteo believes the pressure of managing Barca may have influenced Guardiola's decision.
“He knows what he does,” the Italian coach told reporters on Friday. “He’s a fantastic person.
“He’s had such tremendous success and he has decided what is probably best for himself, his career and maybe his family.
“I would say the pressure [got to him]; you have that in every club because of different targets but you have the pressure in his position.
“What a coach, what a manager he is. If he’s decided to not want to continue at the end of the season, he’s a great guy and he’s a young man as well and he’s still got many years ahead of him.”
Guardiola’s 13 trophies in four years at the Nou Camp is a phenomenal and unprecedented run of success, but the Italian doubts the Spaniard will be able to replicate his achievements with Barcelona at another club.
“I think he’s a role model as a coach for every young manager,” the former West Brom boss added.
“What he has achieved in such a short period of time I’m not sure anyone else can actually replicate that. History tells us that it’s difficult to replicate the culture of a club into a different club.
“So he might be the first to do it but if you look back at the history of football it’s proven very difficult to do it.”
Having stepped up from assistant manager when Andre Villas-Boas was fired at the start of March, Di Matteo has become a popular choice for the managerial job full-time.
The Italian remained focused on the task at hand when asked by reporters where he stands on the issue, saying: “Nothing has changed from my point of view.
“I’m still very happy to be able to get this club to the end of the season and then this club will make a decision on what is best for the club.
“Like six weeks ago, I’m very relaxed about that [his future]. It’s irrelevant at this point of the season."
Gary Cahill had to come off the Nou Camp pitch after 12 minutes on Tuesday with a hamstring problem and Di Matteo confessed the club is unsure when the center back will be fit again.
“At the moment we hope that he’s going to recover as quickly as possible,” he said.
“That’s our hope and that’s what our aim is with the medical department. When he’s going to be fit we cannot say at this moment in time.”