Former SF 49ers star Chris Borland is getting MAJOR support from his family for his decision to walk away from the NFL over head injury concerns -- with his mom telling TMZ Sports, "I'm extremely proud of him."

Borland's decision made headlines all over the country -- especially since he was a rising star in the league, only 24 years old, and left nearly $2 million on the table by not finishing out his contract.

But his mother Zebbie says Chris didn't take his decision lightly -- noting that he consulted with his parents and other family members before deciding to walk away from the league.

"He made the decision the other day. He's been here [Dayton, Ohio] a ton and on the road visiting his friends and siblings and the decision was made amongst the family."

"Right now he and his dad are handling the situation going forward and deciding on what his next steps will be."

As for how Chris' decision will affect other family members who want to play football, Zebbie says ... "I know Chris' 4-year-old nephews will end up playing sports soon, I'm sure he won't discourage them from playing football, I think he will work with them and provide knowledge."