The Real Madrid midfielder appeared to be carrying a knock after the 0-0 draw against Slovenia.
But Southgate said: "When you are walking off the pitch and have given everything you feel in a certain way, physically and emotionally. Jude missed a period at the end of the season with an ankle injury so he will have benefitted form the matches he has had.
"Of course we have to be mindful of the quality we have to come into the game, freshness might make a difference in the latest stages of matches. But I am not concerned about Jude Bellingham's condition, today is a big day for him (Bellingham's 21st birthday) and a reminder of how well he deals with the expectation around him at a remarkably young age.
"There are few players who have had to live in that world, his world is different to most 21 year olds."