Phil Foden, Harry Maguire, Declan Rice and Kalvin Phillips would all be ruled out of a last-four encounter against either the Czech Republic or Denmark if they picked up another booking when the Three Lions meet Ukraine in Saturday's quarterfinal at Rome's Olympic Stadium.
England are favourites to progress to the final as the highest rank team left in their half of the draw, while they have lost just one of their seven meetings with Ukraine, winning the only previous Euros clash 1-0 in 2012.
However, asked by ESPN whether the yellow card situation would affect his team selection against Andriy Shevchenko's side, Southgate replied:
"No. I don't really understand that rationale. I understand that strategically you might like to do that but I can't think of a country in the world that would do that for a quarterfinal.
"And especially not a country that has only been to three semifinals in its history. No, I think we've got to focus on tomorrow. I think it would be a big error for us to be thinking about anything else and I think it would be an insult to Ukraine as well.
"So, we won't make any decisions based on yellow cards. We did in the last group game because we knew we had qualified and we had the opportunity to protect Phil within that game because we weren't sure what was going to happen further on. But now we play to win and we have got to have everybody available."
The game kicks off at 9 p.m. local time, but temperatures in the Italian capital are still expected to reach 25-degrees-Celsius. England have habitually struggled to cope with such conditions given their lack of exposure to warmer climes during the domestic season, but Southgate is drawing confidence from their Group D opening win over Croatia at Wembley. Temperatures in that afternoon match when reached a yearly high in the United Kingdom of 28-degrees-Celsius.
"I don't think it will be as hot as the game with Croatia and of course the sun will be going down," he said. "We will be playing in the evening which will give some respite I think. I think we are definitely used to handling those sorts of conditions. It will be important to use the ball well.
"That's for certain and we've got all the sort of cooling strategies and rehydration strategies that any team would have really."