Wide receiver Austin Collie, who sustained a concussion Sunday against the Jacksonville Jaguars, was placed on injured reserve Wednesday.
Though Collie is in his second year, Manning feels as if he's losing a veteran. Despite missing five games and more than a half in three others, Collie leads all Colts receivers with eight touchdown catches and also is second in receptions (58) and third in yards (649).
"He's fast, he's got a good feel for zones, he understands defenses," Manning said. "He has his physical talents, but also, his experience has helped him play at such a high level at such a young point in his career."
Collie was injured late in the first half against the Jaguars when he collided with linebacker Daryl Smith while going low to make a catch. It was Collie's second concussion of the season.
Manning already had lost tight end Dallas Clark and wide receiver Anthony Gonzalez for the season, and running back Joseph Addai missed the previous eight games because of a shoulder injury. But the Colts (8-6) are fighting for a playoff spot and don't have time to feel sorry for themselves entering Sunday's game at Oakland (7-7).
"It doesn't do you any good to think about who's not playing and who's not going to be available," Manning said. "You have to go with who's available, and feel like with who's available, you can go out there and still make things happen."
Collie began to emerge as a go-to player when he caught seven passes for 123 yards and one touchdown in last season's AFC Championship Game against the New York Jets. He caught 11 passes for 163 yards and one touchdown in the opener this season against the Houston Texans, and two weeks later, he caught 12 passes for 171 yards and two scores against the Denver Broncos.
Collie's first concussion was the result of a scary collision during the second quarter Nov. 7 at Philadelphia. He didn't play against the Cincinnati Bengals the next week, then returned against the New England Patriots the following week before leaving that game because he felt uncomfortable. He sat out against the San Diego Chargers, Dallas Cowboys and Tennessee Titans before trying again Sunday. He caught eight passes for 87 yards against the Jaguars before the hit by Smith.
"Obviously, it's disappointing for him," Manning said. "I know how hard he's worked all offseason. I know how excited he was to be back the other day, and how well he was playing."
Blair White will step into Collie's role. The rookie has 30 catches for 284 yards and three touchdowns. Caldwell said White's experience this season should make the adjustment easier.
"I do think that there are times when we talk about how, if we embrace a situation that occurs where we do have someone absent and we are able to develop some depth that somewhere down the line, that maybe, that's going to help you," he said.
Collie is the 17th Colts player placed on injured reserve this season, yet Indianapolis is two wins away from another AFC South title.
The Associated Press contributed to this report.