Indianapolis Colts wide receiver T.Y. Hilton is being evaluated for an upper back/neck injury, sources told ESPN's Adam Schefter, and it is uncertain how much time he will miss.

Hilton, 31, has been the Colts' No. 1 receiver throughout his nine seasons in Indianapolis, which includes five 1,000-yard campaigns.

A free agent this past offseason, Hilton signed a one-year, $8 million contract to return to Indianapolis. He is guaranteed $8 million and can earn up to $10 million if he reaches incentives. He said he turned down a multiyear deal with the Baltimore Ravens to remain with the franchise.

"I wanted to stay here no matter what the cost was," Hilton said in April. "I gave up a lot of money to stay here and that's what I wanted to do."

In April, Hilton was asked by reporters if this season might be his last.

"After this one year, I'll reevaluate everything, see how my body's feeling," he said. "If I want to keep going, I'll keep going and if not, I'll hang it up."

Hilton led the Colts in receiving yards with 762 last season and tied for the team lead with five touchdown catches.