Manchester United and England defender Luke Shaw was stretchered off 54 minutes into the UEFA Nations League match against Spain on Saturday with what the English FA has called a concussion.
The game was stopped for over five minutes while Shaw received treatment following a clash with Dani Carvajal. He landed heavily on the ground after the collision with the Real Madrid man and appeared to be knocked out.
A Football Association spokesperson said that Shaw was "fine and walking and talking in the dressing room" soon afterward.
The FA then confirmed on Sunday that Shaw had remained at St. George's Park after sustaining a concussion and would return to Manchester United on Monday.
Following the match, England had tweeted from their official account: "Luke is awake and alert, having been assessed by our doctor and given an X-ray."
Update on @LukeShaw23:— England (@England) September 8, 2018
Luke is awake and alert, having been assessed by our doctor and given an X-ray.
He'll stay with us overnight for further observation, with another update to come in the morning. pic.twitter.com/OZ7EV1SDWb
Shaw tweeted to fans after the match: "Thank you for all the love and support I am doing fine and am in the best hands. I'm a fighter so I will be back soon!"
Gareth Southgate also weighed in on Shaw's injury after the match, saying the team wouldn't take any chances as he continues treatment.
"He's sat up in the dressing room. He's talking and seems fairly comfortable," Southgate said. "We'll have to assess him a little bit more overnight and tomorrow, but that's definitely a good sign."
Southgate also said it was "difficult to tell" if Shaw had lost consciousness on the pitch after the collision, adding: "We'll go through some tests. It's obviously a nasty-looking fall and collision.
"For certain, we won't take any chances with his health but the good news is he is awake, talking and seems reasonably fine."
Shaw, 23, was winning his eighth cap for his country, and the first since March 2017 after being recalled following a strong start to the season with United.
The left-back had set up Marcus Rashford to put England in front in the 11th minute, with United manager Jose Mourinho in the stands at Wembley watching on.
Meanwhile, England have called up Leicester City duo Ben Chilwell and Demarai Gray for Tuesday's friendly against Switzerland at the King Power Stadium, the FA said on Sunday.
Chilwell and Gray will not travel out to Latvia with the England Under-21s squad on Monday and will join Southgate's senior squad for the first time.
Left-back Chilwell replaces Shaw while forward Gray could replace United's Marcus Rashford who also picked up a knock against Spain.
Reuters contributed to this report.