Sources with direct knowledge tell TMZ ... Chance is set to put on her cap and gown Thursday for her graduation from Sierra Canyon School in the L.A. area -- and while we're told other family members are flying in for the ceremony, her dad won't be present.

We're told Diddy's already communicated this news to the family, although he did not offer any exact reason for his absence -- but it can't be all that shocking to them.

We're told the family suspects it has to do with all of his legal issues these days, and his desire to lay low. Makes sense ... if Diddy showed, it could easily turn into a spectacle that would steal Chance's thunder.

Now, in terms of who exactly will be in attendance for Chance's graduation ... our sources say some of her half-siblings are supposed to be there, as are some of Kim Porter's family too. Diddy shares Chance with Sarah Chapman.

BTW, Chance isn't the only child he has in high school right now -- Jessie and D'Lila, the twins he had with Kim, are juniors who went to prom a couple weeks ago ... an event Diddy also missed, as he remains in Miami.

We should note, Diddy's been a pretty involved parent with his kids over the years -- especially for the girls, who were actually with him when the raids went down back in March.

You'll recall, he was getting ready to take them on Spring Break when the feds intercepted his private jet in Florida. He's remained at or near his Miami home ever since then.

Sources with direct knowledge tell TMZ ... federal authorities have not restricted his travel in any way shape or form.

Translation: The fact he's missing big moments for his children is entirely his choice, not something mandated by law enforcement.

Fact is, Diddy might be on the verge of getting indicted, and while he's tried continuing on as normally as possible ... it's frankly a precarious time, and it sounds like he's trying to avoid roping his kids into the drama.