The Reds need victory to keep the title race alive, with Manchester City currently leading the table by four points, having played a game more.
Klopp said: "This process is not finished yet because we only played the 120 minutes two days ago.
"We have a lot of decisions. We will line up a team with one reason. To try and win the game at Southampton.
“We have to see who is able to help, the 30 extra minutes made a big difference. We will have to see."
Klopp continued: "I don't know the last time City dropped points two games in a row. Villa have to play midweek. They are not used to that.
"City is a pretty good football team and I don't expect them to drop points there. But this has no influence on our game for tomorrow.
"In an ideal world we go into the last match one point behind.
"If we play a season like we play and we win the Carabao and fight for the title until the end, I think it's a good season.
"The FA Cup is a massive competition. It felt great. It takes pressure off and that's what makes it more enjoyable.
"It would be massive if we win in a few weeks' time in the Champions League. But we play the most experienced Champions League team on this planet.
"We aren't massive favourites. It's an open game and every little advantage we can get is good. They win the league already. Between now and then, two massive games."
He added: "This is game 60 so we have to be very careful. We don't finish the season tomorrow.
"We have to make changes. I don't know how many."
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