KANSAS CITY, Mo. >> Chiefs quarterback Alex Smith will miss Sunday’s game against the San Diego Chargers because of a lacerated spleen, he said Friday.

Chase Daniel will start in his place with both teams seeking a playoff spot.

Smith was likely hurt on a hit early in the third quarter of last weekend’s 20-12 road loss to the Pittsburgh Steelers, but he didn’t feel any pain at the time. He wasn’t diagnosed until undergoing a scan Thursday after several days of what felt more like a stomachache than a serious injury.

The quarterback will not need surgery and is expected to fully recover, but Smith would miss a potential playoff game.

If the Chargers beat Kansas City, they clinch a postseason berth. The Chiefs would need to win and have Baltimore and Houston lose to make the playoffs.

Daniel has one career start in six NFL seasons — which happened to come against the Chargers in last year’s regular-season finale. With the Chiefs locked into the No. 5 seed, Smith rested that day. Daniel went 21 of 30 for 200 yards with a touchdown and no interceptions and rushed seven times for 59 yards in a 27-24 overtime loss that got San Diego into the playoffs.

Smith didn’t notice anything was amiss Sunday until after he’d showered and the adrenaline wore off. Experiencing cramping and pressure, Smith visited the medical staff, but he didn’t exhibit the telltale signs of a lacerated spleen.

“Thought it was something I ate,” he said, so he took some antacids.

Smith practiced twice this week, feeling fine other than some nausea. A stomach virus had been going around the team, so everyone suspected it might be that.

By Thursday, though, he hadn’t gotten any better.

“It just didn’t go away,” he said.

Smith didn’t want to leave his family on Christmas, but a team doctor helped persuade him to undergo the scan, which found a 3-centimeter laceration. Smith had little bleeding, explaining why he had so few symptoms.

If Smith had taken a hard hit to the abdomen after the injury occurred, his spleen could have ruptured, causing dangerous bleeding.

Smith believes he was hurt when he was hit by linebacker Jason Worilds after releasing an incomplete deep pass to Albert Wilson on the Chiefs’ first drive of the second half Sunday. Team trainer Rick Burkholder said nothing about the play looked out of the ordinary live or when he later rewatched it on video.

Smith was 15 of 23 for 125 yards after that, leading the Chiefs to two field goals.

Smith has thrown for 18 touchdowns with six interceptions this season.