Rivera said the Panthers need to clear salary cap room and said free agency may determine Smith's fate.
Smith, the franchise's all-time leader in receptions and touchdowns, is under contract through 2016 but is set to cost $7 million under the 2014 NFL salary cap.
A 13-year NFL veteran who holds almost every major receiving record with the Panthers, Smith was present at Gross' retirement news conference but declined to discuss his own future. "This is Jordan's day," Smith said. "We're not discussing me."
Smith plans to meet with general manager Dave Gettleman soon to determine what his future holds. It's unclear if the Panthers want Smith to take a pay cut.
Carolina has restructured the contracts of linebacker Thomas Davis, center Ryan Kalil and running back Jonathan Stewart this offseason to create cap space.
The Panthers need to create cap room to sign quarterback Cam Newton to a long-term contract extension and also need to make a decision soon on the future of defensive end Greg Hardy, who'll be an unrestricted free agent.
Restructuring contracts has become commonplace in the Gettleman regime. He restructured seven contracts last season, including Gross' deal.
"I didn't like you very much last offseason, but I got over that," Gross joked to Gettleman at the news conference.
Rivera said he thinks Smith, who had 64 receptions for 745 yards and four touchdowns last season, wants to stay in Carolina.
The news conference for Gross was attended by team owner Jerry Richardson and more than three dozen former teammates, coaches and members of the training staff.
Gross looked more like a tight end than an offensive lineman, already having dropped 25 pounds from his regular playing weight of 305.
An emotional Gross presented a slideshow with some of his favorite photos through the years often making fun of himself along the way. He got choked up when he got to a picture of team's offensive linemen and then again when he saw a photo of Smith jumping into his arms during the Super Bowl.
After Gross finished speaking he got a huge surprise when a Charlotte-based barbershop quartet led by Kalil stood up and sang "Happy Trails."
"This wasn't your typical retirement press conference," Gross said with a laugh.
Former Utes have made Carolina home
P Former University of Utah standouts Jordan Gross and Steve Smith were the only two on last year's roster who played for Carolina's Super Bowl team in 2003.