Jadon Sancho and Tammy Abraham are back in England contention again after missing Thursday's friendly win over Wales due to breaching coronavirus protocols.
Sancho, Abraham and Ben Chilwell were left out of the squad for the 3-0 victory after it emerged earlier in the week they had attended a party last Saturday.
The trio were filmed attending Abraham's 23rd birthday party at his home in London on Saturday, in clear violation of the "rule of six" designed to contain the spread of coronavirus across the country.
All three players have since issued an apology, with Southgate confirming the trio would be missing for at least the Wales friendly.
Southgate said their availability to face Belgium in Sunday's Nations League encounter depended on them passing UEFA-mandated coronavirus tests two days before, and they were given the go-ahead to return to training on Saturday.
"Tammy and Jadon both trained this morning, so everyone is available," Southgate told reporters.
"They've obviously missed a bit of training, so that's a bit of a concern in terms of their load through the week but no, it [the punishment] is done, that situation is done.
"They are back with the group and we move forward."
Chilwell remains a doubt for Sunday's match, however, as he was unable to take the UEFA test on Friday due to a non-coronavirus related illness.
"Ben will be tested today and we have to wait for the results of that test tomorrow and then we can make a decision from there medically on that," Southgate added.
A player who impressed in Sancho's absence on Thursday was Jack Grealish, who set up Dominic Calvert-Lewin's opener on his first England start.
But Southgate was eager to calm comparisons between Aston Villa playmaker Grealish and Three Lions great Paul Gascoigne.
"I'm very conscious, I don't want to be dampening the enthusiasm for Jack, I always answer honestly about people, but when you talk about Gascoigne, there's not a player in English history at that level, in my opinion," he said.
"But I don't want that to be seen as a criticism of Jack. In many ways, Gascoigne was unique, such an incredible player, it's a bit like talking about Bobby Moore.
"I think what we have to say is, young players who come through, we shouldn't burden them with comparing them to someone else, their own talents are unique.
"I kind of understood some of the comparison, but I think Gascoigne was on another level to anyone else I played with."