Sources: Colts' Michael Pittman Jr. (back) to miss multiple weeks

INDIANAPOLIS -- Michael Pittman Jr., the Colts' No. 1 wide receiver, has suffered a back injury that is expected to sideline him for multiple games, sources told ESPN's Adam Schefter on Wednesday.

Pittman played the entirety of Sunday's loss at the Jacksonville Jaguars but is believed to have been injured in the game. He joins a long list of key Colts players dealing with injuries, leaving them looking for answers at numerous positions.

The Colts have not yet determined whether Pittman will be placed on injured reserve, which would sideline him for at least four games.

Pittman has 22 receptions for 238 yards and a touchdown through five games this season and has 3,159 combined receiving yards in the past three seasons. He was rewarded during the offseason with a three-year, $70 million contract extension in March that prevented him from reaching free agency.

Also Wednesday, the Colts said starting receiver  Josh Downs is dealing with a toe injury. He was a non-participant in practice.

Pittman's absence will put the spotlight on third-year player Alec Pierce, who has thrived as a deep threat this season -- he leads the NFL in yards per reception at 28.3 -- but now is likely to be asked to run a wider variety of routes. Rookie Adonai Mitchell is also likely to see more opportunities, though he'll need to be sharper after posting just six catches on 20 targets this season.

Pittman's injury compounds an already concerning injury situation for the Colts.

Quarterback Anthony Richardson is working his way back from an oblique injury that sidelined him in Week 5, star running back Jonathan Taylor is out with an ankle injury, starting defensive end Kwity Paye has missed two games with a quad injury and standout defensive tackle DeForest Buckner is on injured reserve with a high ankle sprain.