Lehmann said after Monday's practice that the ball was too fast and slippery when it rains.
"It may be good for the outfield players and for the crowd, but not for the goalkeepers," Lehmann said.
The World Cup ball is made by Adidas and is officially known as Teamgeist (Team Spirit) - which has been the rallying cry of the German team as it prepares to host the World Cup.
"When it rains it's going to be very uncomfortable for us," Lehmann said. "It gets very slippery and flutters in the air."
The ball made by rival manufacturer Nike didn't get high marks from Lehmann either.
"Both of them make the goalkeepers look bad," he said.
Lehmann joined the team Sunday in Geneva, after it flew in from Sardinia, where Germany conducted the first stage of its World Cup preparations that focused on improving fitness and did not include any practices with a soccer ball.
The Arsenal goalkeeper was excused from the first stage because of the Champions League final against FC Barcelona. Lehmann was sent off after 18 minutes when he brought down Samuel Eto'o, and Barcelona rallied for a 2-1 win.
"The important thing is that I am here with the squad, to prepare well and to follow the common goal - that's enough to forget the last game," Lehmann said.
Germany coach Juergen Klinsmann decided last month to make Lehmann his No. 1 goalkeeper, demoting longtime starter Oliver Kahn to the bench.
"I've been rewarded for all the hard work, especially in the last two years," Lehmann said. "But it's not especially important for me to be No. 1. I've now played the quarterfinals, the semifinals and the final of the Champions League and they were a lot of fun.
"I now feel very motivated to play more matches like that," Lehmann added.
Lehmann said he had breakfast in the team hotel with Kahn. The two rivals have had a tense relationship for years and have not been friends.
Team officials have said that Kahn was in a relaxed mood and having a positive influence on younger players. Kahn and Lehmann are both 36 and by far the oldest players on Klinsmann's young squad.
Striker Lukas Podolski practiced Monday after overcoming back problems, as well as midfielder Sebastian Kehl, who had an ankle injury.
Defenders Philipp Lahm and Christoph Metzelder are still only doing light training. Lahm had surgery on his elbow last week, while Metzelder is nursing a calf injury.
Germany will stay in Geneva until May 30, but will go home for a short trip to play Luxembourg in Freiburg on Saturday.
On May 30, Germany plays Japan in Leverkusen and on June 2 it plays Colombia in Moenchengladbach. The hosts kick off the monthlong World Cup against Costa Rica in Munich on June 9.Reuse content