Neither Kittle nor Garoppolo returned to the 37-27 defeat, and their status for Thursday night's home game against the Green Bay Packers is up in the air until they are able to get further testing on Monday, according to coach Kyle Shanahan.
Kittle and Garoppolo's injuries came within minutes of each other early in the fourth quarter, and both retreated to the locker room in Seattle for further examination. Both were listed as questionable to return but did not make it back onto the field. Those injuries came after running back Tevin Coleman left in the first quarter with a knee injury.
Garoppolo seemed to tweak his ankle earlier in the game but played through it before he was removed with 14:02 left to play. He limped to the locker room after going 11-of-16 for 84 yards with no touchdowns and an interception for a passer rating of 55.2. Nick Mullens stepped in for Garoppolo.
Another ankle injury sidelined Garoppolo earlier this season. He sustained a high right ankle sprain in Week 2 against the New York Jets, an injury that cost him the two games that followed and part of a third game the next week after he struggled in his return against the Miami Dolphins.
"I knew it was hurt once we all saw it and he didn't go back in on that one play," Shanahan said. "He had a good week of practice throwing, but high ankle sprains linger, so you never know when it's going to affect you. I know he hurt it later in the game, or re-hurt it, and we'll wait until tomorrow to see how bad it is."
Kittle's foot injury came with 12:36 to play after he leaped to haul in a 25-yard pass from Mullens. Kittle made the play but came down awkwardly on the ankle and hobbled to the sideline soon after. Initially thought to be an ankle injury, the 49ers said it was a foot issue for Kittle.
Kittle finished with two catches for 39 yards; Ross Dwelley replaced him and caught a 16-yard touchdown pass.
"Nothing was broken at least on the X-rays, so we've got to check MRIs and stuff tomorrow," Shanahan said.
One day after the Niners activated Coleman, who had spent the previous five games on injured reserve with a sprained knee, the running back was unable to make it through the first quarter of the game Sunday.
With 5:42 left in the first quarter, Coleman took a handoff to the left side and gained 12 yards on second-and-10. But Coleman got up slowly and hobbled to the sideline immediately after the play.
At halftime, the Niners said Coleman was questionable to return with a knee injury, but they ruled him out soon after. Coleman had three carries for 20 yards before departing.
"It was the same knee," Shanahan said. "He wanted to go back in. We tried, and he just couldn't. I don't know what the deal is for this week. Obviously, I'm hoping he's ready for Thursday, but his knee was reinjured, and he couldn't go back in the game."
The loss of Coleman left the Niners with just rookie JaMycal Hasty and veteran Jerick McKinnon available at running back. McKinnon has had a limited role in recent weeks after a heavy workload early in the season, leaving Hasty to get many of the opportunities.
Hasty scored his first NFL touchdown in the second quarter and finished with 12 carries for 29 yards. McKinnon had three carries for negative-1 yard and caught four passes for 40 yards.