SEATTLE — Jimmy Garoppolo will face a Seahawks secondary Sunday that won’t have dynamic free safety Quandre Diggs.
Seattle was holding out hope Diggs could play against the 49ers after he sustained a high ankle sprain on Dec. 15. Diggs was listed as questionable, but he’s been unable to practice since the injury.
Diggs has three interceptions, three pass breakups, a forced fumble and a fumble recovery in five games since he was acquired in a trade with the Lions.
The Seahawks’ pass defense ranks 27th in the NFL, allowing 263.5 yards a game, and they’ve had major issues covering tight ends: They have allowed the fourth-most catches (90) and second-most yards (1,013) to tight ends this season.
Pro Bowl tight end George Kittle (78 catches, 967 yards) didn’t play in Seattle’s 27-24 overtime win against the 49ers in November.
Alexander update: Inside linebacker Kwon Alexander, who suffered a torn pectoral on Oct. 31, went through a workout overseen by trainers before the game.
The 49ers haven’t ruled out Alexander being able to return if they make a deep playoff run.
Texans defensive tackle J.J. Watt, who suffered a torn pectoral on Oct. 27, returned to practice Tuesday and is expected to return for the Houston’s wild-card game.
“It would be awesome if he could (return),” head coach Kyle Shanahan said of Aklexander on Dec. 17. “But it’s a really big injury, and that would be down the road. So there would be an outside chance at it … we haven’t ruled it out.”
Inactives: Anthony Zettel, who was signed Dec. 23, and undrafted rookie Kevin Givens, who was promoted from the practice squad Saturday, will be two of eight defensive linemen in uniform Sunday.
The 49ers’ inactives are: safety Jaquiski Tartt (ribs), defensive end Dee Ford (hamstring), running back Jeff Wilson, cornerback Dontae Johnson, tight end Daniel Helm, wide receiver Jordan Matthews and quarterback C.J. Beathard.
Eric Branch covers the 49ers for The San Francisco Chronicle. Email: ebranch@sfchronicle.com Twitter: @Eric_Branch
