Henderson, 30, was ruled out of action for Liverpool and England since February due to a groin injury.
Henderson was brought off the bench to replace Kalvin Phillips in England's 1-0 win over Romania at the Riverside Stadium on Sunday.
Speaking ahead of the match, Keane pulled no punches towards the England international and wasn't convinced with his place in the Three Lions squad.
The 49-year-old Irish pundit told ITV: "I was convinced Jordan was going to play the other day.
Roy Keane on Jordan Henderson... :grimacing:- ITV Football (@itvfootball) June 6, 2021
"Clearly Jordan's not fit - I don't think he should be involved... I've heard people say they want him around the place - for what? Does he do card tricks? Does he have a sing song? Does he do quizzes in the evenings?" pic.twitter.com/YhYaXxg8FX
"I think it's a huge distraction -- he's clearly not fit. I don't think he should be involved.
"If he can't start against Romania, he's not fit. Physically and mentally, this game won't be that tough for him to deal with, he's an experienced player.
"He's not kicked a ball for three-and-a-half months and he's going to [the] European Championship? He can't be right."
Keane continued his extraordinary rant by saying that Henderson "doesn't want to be around the place being some sort of cheerleader."
The Manchester United legend added: "I've heard a lot of people say they want him around the place. For what?
"Does he do card tricks? Does he have a sing-song? Does he do quizzes in the evening? What does he do?
"Liverpool won't be happy either. Surely Jordan doesn't want to be around the place being some sort of cheerleader, you want to play and clearly he's nowhere near it."
Southgate insisted that they were not "distracted by anything" and claimed Henderson has been a "very positive influence around the camp."
When asked about Keane's remarks, the England boss said at his post-match press conference: "Well, I think firstly we are not distracted by anything.
"We know the situation Hendo is in, he's been a very positive influence around the camp with the group.
"It's a step forward for him physically today, which was important for him to be able to play some sort of part in the tournament and we are realistic about what that could be.
"It's not a situation where it's dividing the group or it's unrealistic what's possible.
"We're not hanging our hat on him being fit and if we can get him to a good level, then that's a bonus. We've got 26 players, which hasn't been the case before.
"With the penalties, we are very diligent in how we practise them. I didn't expect what happened to happen and I wouldn't expect that to happen again."
Henderson left England fans furious with his post-match comments after he laughed off his penalty miss against Romania.
Southgate admitted that he was not happy with the Liverpool star taking the ball off Dominic Calvert-Lewin to take the penalty, saying that he "will have to check what happened."
Featured Image Credit: ITV/PA
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