Second-placed Dortmund, who are a point behind leaders Bayern Munich, visit Arsenal on Tuesday and Klopp has to balance domestic and European commitments and a growing injury list.
Marcel Schmelzer and Marco Reus both had to withdraw from international duty due to knocks which continue to linger while Nuri Sahin is also a doubt.
"I'll group my troops together on Friday and then I should know who can play, and you'll find out on Saturday," Klopp said at the pre-match press conference.
The Dortmund coach insists that neither the Arsenal game, nor the Revier derby with Schalke next weekend, will play a part in his plans, although he stressed he would not take any risks with his walking wounded.
"For sure if things are touch and go, we'll leave a player out," he said. "If we had an additional player for every position, then it would be worth considering changes, but the way things are, we can't do that.
"Resting somebody who then goes and runs head on into the post in training on Sunday would make no sense either."
Hannover coach Mirko Slomka may have only one injury concern, but it is an important one.
Mame Diouf returned to training this week and is in line for his comeback, but having seen him last only 19 minutes on his last return to action after injury, Slomka will be wary about throwing him back in at the deep end.
"Mame has got to be certain - we can't take any risks," Slomka said. "He can play only if the doctors give the green light."
Didier Ya Konan is sidelined for the visitors while Artur Sobiech missed international duty in midweek through injury and will be assessed before the game.