The sudden concern over Cliff Avril’s health — and thus career — has put the spotlight on the future of Seattle’s defensive line.

Almost exactly 10 years ago, Mack Strong faced a similar neck injury and decided to immediately call it a career (after 15 years). Avril, injured against the Colts on Sunday, might face the same choice in his 10th season. He is out indefinitely as he and the team investigate the cause of the stingers that numbed his arms and hands after he was kicked in the chin tackling Jacoby Brissett.

“Whenever it’s the spinal stuff and you get stingers, that means that there’s some nerve action going on there and you’ve got to be really careful and really safe with all that stuff,” Pete Carroll told KIRO Radio on Friday. “In this case in particular, we’ve just got to make sure, so we’re going to take our time with this and let it quiet down. He’s really not uncomfortable, but just some of the tests he took showed some stuff and we’ve just got to make sure we’re really honoring it and make good choices here. We’re on the same page and (will) take it one step at a time, and we’ll get to it when we can.”

It’s entirely possible Avril will return soon — maybe even after the Week 6 bye. But the 31-year-old also might decide after this injury that the ongoing risk is not worth it anymore.

On Wednesday, asked if this is a long-term issue, Carroll said, “Could be. We are going to go very slowly and make sure that he takes all the opportunity to talk to as many people as he wants to, to make sure he knows what he’s got and what we need to do with it. We are just going to take care of him and make sure that he is well. And if he wants to come back and we want to bring him back, we’ll let you know when we know. But right now we don’t.’’

In the short term, whether it’s one game or the rest of this season, Avril’s snaps will be taken by Frank Clark and Marcus Smith (who had 1.5 sacks vs. the Colts).

If Avril does end up retiring — immediately or after the season — the team will have to look toward replacing him a year earlier than expected (he is signed through 2018).

Clark would be a natural choice. He is signed through 2018 as well; and, if the team is content with his off-field maturity, he could be in line for an extension next offseason. Avril’s $7.5 million in 2018 pay could go toward that. Seattle also might choose to re-sign Smith and let Clark play out his deal.

As we have said before, John Schneider will need to make some key roster decisions next year.

Sheldon Richardson will be one of the biggest. Schneider surely will try to keep him, but at what price? Richardson figures to command at least $15 million a year. The Hawks could afford it, if they part with guys like Jimmy Graham, Jeremy Lane and Luke Joeckel. But will they want to pay it?

Schneider also has to consider extensions for Earl Thomas, Richard Sherman, K.J. Wright and Tyler Lockett while weighing offers for about 15 free-agent role players.

If Avril calls it a career on top of that, replacing him long term will be one more thing added to Schneider’s to-do list.