Germany kick-off their Group G campaign in Salvador on Monday, but the 28-year-old Neuer had been a concern after receiving intense treatment since injuring his shoulder for Bayern Munich in the German Cup final four weeks ago.
"He's doing really well and he's completely ready to play," said Koepke.
Germany's goalkeeping coach said they had not been taking any risks with Neuer's injury, but "Manuel has confidence in the shoulder and things are good for the first World Cup match".
Borussia Dortmund goalkeeper Roman Weidenfeller deputized for Neuer in Germany's warm-up matches against Poland, Cameroon and Armenia, but Neuer is now ready to regain his place.
"We wouldn't take a risk on him, when he plays he will be 100 percent ready to play," said Koepke.
Germany head coach Joachim Loew has all of his 23-man squad available.
He put them through their paces at 1600 GMT at their Santo Andre training base yesterday in 26 degree temperatures and 82 percent humidity to simulate the conditions they will face against Portugal.
"It's about sleep patterns and also getting used to food intake," explained Koepke with the Portugal match to kick-off at 1600 GMT in Salvador.
"We want the players to find out what is right for them. They can get brunch from 0700 until 1030, to test out what and how much they can eat, so they are ready for a 1300 kick-off,” he said.
"On Friday, we will do it again, then on Monday it will be the real thing," he added.


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