Kyle Walker fears he could be near the end of his international career after being sent off during England's 1-0 win over Iceland in the Nations League.
The Three Lions overcame their Euro 2016 tormentors when a turgid affair exploded into stoppage-time drama – Raheem Sterling winning and converting a 91st-minute penalty as Sverrir Ingason joined Walker in receiving his marching orders before Birkir Bjarnason missed a subsequent spot-kick for the hosts.
England's increasingly laboured attempts to secure victory before that point were thrown into flux when Walker, already booked, launched into a rash challenge on Arnor Ingvi Traustason with 20 minutes remaining.
A mainstay of England's run to the semi-finals of the 2018 World Cup, Walker did not feature for his country last season.
In that context and considering competition from the likes of Trent Alexander-Arnold, Kieran Trippier and the as-yet uncapped Aaron Wan-Bissaka, the 30-year-old Manchester City defender acknowledges his error could come with significant ramifications.
"To get sent off for your country is never a nice moment, especially after being out of the team for so long," Walker told Sky Sports.
"I have to take full blame. I'm an experienced player and I should know when I'm on a yellow card not to make a rash challenge like that.
"It's unacceptable from me.
"[Wanting to impress] possibly plays a big part in it but I don't want to blame that. I'm a seasoned professional and I've played a lot of games.
"So I should know how to manage a game if I'm on a yellow card. I put myself in a situation I shouldn't have been in. I think you have to say fair play to the lads for digging in and fighting and getting the win we desperately wanted."
Walker's City team-mate Phil Foden made his England debut with an assured showing in midfield, while Manchester United teenager Mason Greenwood came off the bench for a first senior cap – underlining the ever-evolving options at Southgate's disposal.
"It's brilliant for English football," Walker said. "Throughout the age groups they've gone and won things.
"Phil was involved in the  World Cup win for the under-20. They're proving it at club level for big clubs.
"The world's their oyster. Obviously I know Phil - and Mason seems to be a very good player. He's sharp and can finish so I wish them all the best."
He added: "That's the sad thing about being a footballer. It does come to an end sometimes and I'm probably near the end on my international career
"I still feel very energetic, I feel like I've got a lot in the legs. Hopefully I will be back. It hurts."