Cleveland Browns coach Kevin Stefanski fears that quarterback Deshaun Watson suffered a season-ending Achilles injury during their 21-14 defeat to the Cincinnati Bengals.

Watson will go through tests to confirm a diagnosis for his injury, which he suffered on Sunday.

But Stefanski did not have a great outlook after the game.

"Obviously, it doesn't look good with the injury," he told ESPN.

"I'll give him a call here in a little but ... disappointed for him. Any of our guys that you lose, you're disappointed because you know much this means to them and how hard they work. It's tough."

Watson's injury was sustained during a non-contact play when his leg hyperextended and he fell to the ground.

It compounds a miserable start to the season for the Browns, who are bottom of the AFC North with a 1-6 record.

Fan frustration was noticeable, with many seeming to cheer Watson's injury after he had been booed during the pregame.

"We don't boo guys that are injured on the field, especially when the cart comes out," said defensive end Myles Garrett said after the game.

"We should be ashamed of ourselves as Browns and as fans to boo anyone and their downfall."

Stefanski was in agreement with Garrett.

"I don't think it's ever OK to cheer when someone's injured. I'm sure it's not every person in the building doing that, but that's disappointing," he said.

Meanwhile, it is feared San Francisco 49ers receiver Brandon Aiyuk suffered a torn ACL during their 28-18 defeat to the Kansas City Chiefs on Sunday.

"That's what it looks like, but we don't know for sure," coach Kyle Shanahan told ESPN. "Been wrong before. So, praying that we are [again]."

Further tests will confirm the exact issue and determine whether Aiyuk will miss the rest of the season.

With fitness problems mounting for the 49ers, Deebo Samuel was also announced to be suffering from illness before kick-off but was still expected to play.

He was withdrawn after four snaps with no catches or carries.

"Throat, stomach things, just real fatigued," Shanahan said, on Samuel. "Struggled to breathe, couldn't catch his breath ... he kept trying to fight through it, but once he was struggling with the breathing and everything, we had to shut him down."

Aiyuk's teammates, meanwhile, were vocal in their disappointment at potentially missing the wide receiver for the remainder of the season.

"It sucks," said tight end George Kittle. "I love Brandon Aiyuk, the energy that he brings, what he can do on the football field, routes, catching the ball. He's an incredible football player. You can't really replace, in my opinion, one of the best receivers in the NFL."

Quarterback Brock Purdy echoed Kittle's sentiments.

"What BA does for our offense and who he is and as a teammate and the brother of ours, man, it's sad," he said.

"Wish him nothing but the best and praying for him. So that's my guy. And when he goes down like that, obviously we have other guys that can step up and do their job really well ... we all just got to come together as a group collectively, the receiver unit and all of us."

Aaron Rodgers says there are "no excuses" for the New York Jets after mistakes saw them fall to a 32-19 loss to the San Francisco 49ers in their NFL opener.

Rodgers, making his first appearance since rupturing his Achilles tendon in the Jets' first game of 2023, struggled for much of his return.

He was held to just 167 yards on 13-of-21 passes and had an interception that led to one of five field goals for San Francisco, though he did throw one touchdown pass to Allen Lazard in the third quarter. 

The 40-year-old was less than impressed with his first start in 20 months and is already looking for improvements.

"That's an excuse [none of the starters playing in pre-season]. I'm not going to use that," Rodgers said. "I don't think we should. We expect greatness when we step on the field.

"This is a tough opener for us, travel-wise and schedule-wise, but no excuses. We have to play better, and I have to play better, and we'll bounce back."

Rodgers became just the 22nd quarterback in the Super Bowl era (since 1966) to play after his 40th birthday, and despite the disappointing result, he was pleased to be back out on the field.

"It felt great," he added. "A lot of gratitude just to be back in pads. So many people helped me get to this spot.

"I'm really thankful for my surgeon, my loved ones, my friends, the staff and the training staff to help me get back. Obviously, I wanted to take a shot and feel the physicality of it.

"Once I threw a couple of balls and took a shot, it felt good."

The 49ers played without star running back Christian McCaffrey, who was ruled out shortly before kick-off due to a calf and Achilles injury.

Jordan Mason stepped up in his absence, playing a starring role for the Super Bowl runners-up as he finished with a career-high 28 carries for 147 yards and a touchdown.

"I thought he runs like he always does," coach Kyle Shanahan said.

"When you get him the ball, he breaks tackles, usually gets more than we block for. When we had the good lanes, he always hit them, and we got a bunch."