The assistant boss insists the team will be going all out for the points against his former club and calls on the fans to repeat their superb backing of the players on day.
"We need a big performance and a good result," said John. "We've got to make up for our last two games - especially the Fulham one - and we need the fans to be right behind us and be so supportive on Saturday.
"It is a very, very important game. It is silly to say this so early in the season, but it is. We want to get back into winning ways and, before you know it, people will be looking at the league and seeing how quickly things can change.
"It doesn't take much, pick up the points from two games on the trot and you are right up the table again.
"We need to get a result and we know it is going to be a hard game. Without doubt, Southampton are a very difficult team to beat and there is always an added edge to it when we play them with us having been at the club.
"We are very focused and very determined to get the three points on Saturday."
One factor that gives John added confidence for the forthcoming challenges is the number of players now available for selection.
"The good thing now is that we've got a lot of competition for places. We were able to play 11-a-side with senior players out there and we've got people back in training from injuries like Christian Ziege, Gus Poyet and Robbie Keane.
"This can only be healthy."
John Gorman says there is a determination in the camp to make amends against Southampton on Saturday for recent disappointments.