"It's a sad situation," the 27-year-old Miller told the Houston Chronicle after 10 people were killed and 10 others were injured in the attack by a 17-year-old student, who was charged with capital murder.
"It was a tough tragedy," Miller added. "All the things going on my prayers go out to the families. It's a sad situation.
"You're taking those kids to school and thinking they're going there just to learn and to come back and knowing you lost your child, it's always tough."
The Texans also released the following statement:
"On behalf of the Texans organization, we are saddened by the tragic events at Santa Fe High School this morning and extend our thoughts and heartfelt condolences to the victims, their families, and all those affected," the statement read. "We are grateful for the brave first responders, law enforcement officials and medical personnel. The Texans family will continue to pray for our neighbors."
Miller praised teammate J.J. Watt for offering to cover funeral expenses for the victims' families.
"J.J., he's a great dude," Miller told the newspaper. "He loves the community. He loves to give back to the community. I have a lot of respect for J.J. He's trying to find a way to help the families any way possible during this tough time. I think J.J. did a great thing."
In February, Watt was named the winner of the Walter Payton NFL Man of the Year Award, which recognizes a player's on-field excellence and volunteer and charity work.
Watt led a humanitarian effort to help victims of Hurricane Harvey in August, raising more than $37 million. He started the relief effort with $100,000 of his own money on Aug. 27 while Houston was being hit hard by the flooding.