He said after the 2-1 win over Nigeria: "I think we've been pretty clear for a fair while, but there is real competition for places in certain areas of the pitch".
For Southgate's England the real work starts now in attempting to muster his inexperienced squad into a side that can perform creditably in Russian Federation - because even on today's intermittently sprightly showing the nation can expect no more than that. I have played here many times in so many finals and have managed to have great success here and win pretty much all of the finals I have played.
"Most of them are young - Dele Alli, for example, is 22, just about the same age as Alan Ball was in the (1966) World Cup final, so there is lots of scope and opportunity for someone now to come and produce performances that we will remember for a long time".
Yet this provides more questions than answers and having churned out a solid showing against Nigeria, Butland will need to make sure he doesn't put a foot wrong if he, as expected, starts against Costa Rica in midweek, with Pickford at present perhaps the favourite to get the nod from Southgate in Russian Federation.
England, who also face Panama and Belgium in Group G, qualified for the World Cup easily, winning eight of their 10 matches to finish as unbeaten group winners.More news: USA vows to veto UNSC proposal to protect Palestinians
Nigeria are set to wear their new shirt when they face England in their World Cup warm-up game at Wembley on Saturday (17:15 BST).
"If they produce it for England in a World Cup tournament, it will really bring their career to another level".
Nigeria coach Gernot Rohr said his side could have conceded half a dozen goals in a poor first-half performance which he said reflected a heavy travelling schedule for his players. What is more important is how well they gel as a team and how confidently they get to grips with the tournament.
But a change in formation caused confusion among the England players as Nigeria opted to match their opponents man for man.
Idowu did well to stop Danny Welbeck from feeding off a Dier pass late on as England substitute Marcus Rashford fired a snapshot just wide.
They, apparently, have not forgiven Alli, whose biological father is Nigerian, for shunning the Super Eagles when he was younger.