Titans coach Mike Munchak said Mariani broke both the tibia and fibula in his lower left leg in an gruesome injury that trainers had covered with a pressure wrapping by the time Munchak got out to check on the returner.
"That's something in football you don't want to see, and it's hard to see that and continue on with the game," Munchak said.
Replays showed Mariani's leg snapping near the calf as he went to the ground at the end of 14-yard return with 9:40 left in the first quarter. He remained on the ground for several minutes as a team doctor put an air cast around his lower leg. A few teammates came by to talk with him, and Mariani waved at fans as the cart left the field.
Mariani, a seventh-round draft pick out of Montana, was a Pro Bowl returner in 2010. Munchak called the injury very disappointing after how hard Mariani worked this offseason, turning himself into a receiver Tennessee quarterbacks trusted.
"We saw him being in a great role for that along with the return game," Munchak said. "That's a big loss for us."