Spain manager Robert Moreno has revealed David De Gea chose to keep playing after he suffered a muscle injury in La Roja's 1-1 draw with Sweden on Tuesday.
De Gea limped off after an hour but suffered the injury in the first half.
Per Tony Mogan of the Evening Standard, Moreno said: "He had pain in the abductor muscle, but he received treatment at half-time and wanted to keep playing. He gave us his word, but in the end he couldn't continue."
The goalkeeper appeared to aggravate the issue when he kicked the ball upfield:
De Gea has fallen out of favour in Spain over the last year, and his outing against Sweden was only his third appearance in their last nine matches.
As such, it's understandable he wanted to continue, particularly as he was having an impressive game before he was forced off.
The injury puts him in doubt for the Red Devils' Premier League clash with Liverpool on Sunday, though.
Per Samuel Luckhurst of the Manchester Evening News, it's not often the 'keeper is unavailable for United:
United's No. 2, Sergio Romero, has played just seven times in the Premier League since he joined the club in 2015 and not since the final match of the 2017-18 season.
However, the Argentina international, who has 96 caps for his country, typically does well whenever called upon by the Red Devils.
In his seven league matches for United, he has keep clean sheets in all but one outing.
It will hardly be ideal if De Gea isn't fit to face Liverpool, who have won all eight of their Premier League games so far this season, but Romero is a fine back-up.