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 [2017] 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."