Maguire has been sidelined since suffering ankle ligament damage playing for Manchester United in May, missing United’s Europa League final defeat to Villarreal, England’s two warm-up friendlies and their tournament opener against Croatia last weekend.
But he has taken a full part in training this week and Southgate will pick him in his 23-man matchday squad against the Scots at Wembley.
“Harry will be involved tomorrow, the decision we have got to make is whether he is ready to start,” Southgate said.
“We are really pleased with his progress, he has trained with the team for four or five days now and had no reaction. Each session he is involved in he gets more confident. He is on a really good path.
“We want everyone available, it causes difficult decisions but this morning we had 26 players on the training pitch and that is a great position to be in.
“We know that we have got to compete because otherwise you can get overrun in any game.
“Our focus has got to be on performances getting better with every game we play.
“For the fans and us it is a big occasion but it is another opportunity for three points and our objective is qualification. That is what we have got to focus on.
“In the past we have done that very well. We did that on Sunday, Sunday was a big occasion for everyone and we handled it very well.”
If England can beat the Auld Enemy at the national stadium they will virtually seal their passage to the knockout stages.
Games against Scotland stir up added emotion, particularly with this week’s 25th anniversary of the famous Euro 96 clash between the two clubs, but Southgate says the focus has to be on qualifying.
“We know that we have got to compete because otherwise you can get overrun in any game,” Southgate said.
“Our focus has been on solving the tactical problems that Scotland pose with the way they play, the way they defend, they way they attack.
“Our focus has got to be on our performances getting better with every game we play.
“For the fans and for us it is a big occasion but it is another opportunity for three points and our objective is qualification. That is what we have got to focus on.
“In the past we have done that well. We did that very well on Sunday. Sunday was a big occasion for everyone and we dealt with that really well.”
Southgate, who played in that game made famous by Paul Gascoigne’s fine goal 25 years ago, says he is not going to build up the rivalry with Steve Clarke’s side.
“Every game they play for England means a lot to them, but I think younger generations have a different view on those old rivalries,” Southgate added.
“The history of the games when we were growing up the home internationals were one of the few games you saw live at the end of the season.
“England-Scotland was a massive occasion every year, now it is played less regularly, lots of the players are friends within their clubs.
“I haven’t felt the need to build that up, I want them to approach it like any other game of football and focus on playing well and don’t need to emphasise the other parts too much.”