Schalke are closing in on the signing of Kevin-Prince Boateng from AC Milan while Leverkusen have already agreed a deal with Hoffenheim over the one-year loan of Eren Derdiyok.
The Switzerland striker, who played for Leverkusen between 2009 and 2012, is looking to resurrect his career after being marginalised by Hoffenheim after just one season.
"Leverkusen are just the right club for me to get my career going again," said the 25-year-old.
"I was always happy here and I already know most of the team, and we're playing in the Champions League too.
"This is a great challenge and I'll give it everything to ensure we will be successful this year."
Derdiyok scored 24 goals for Leverkusen in his previous spell there, although the club's director of sport Rudi Voller claimed he could have done even better.
"He was not always able to deliver on his full potential, but we're now giving him the chance to do that," he said. "We're convinced he'll take it."
Derdiyok goes straight into contention for a place in the Leverkusen attack in the battle of two of Germany's Champions League participants.
One other new face could be that of Dennis Aogo, who completed a loan move from Hamburg to Schalke earlier this week.
"I don't know if the coach will pick me, but I'm going to give it my best to help the team," said Germany international Aogo on his new club's website.
"I've only just arrived, but I still think we can get a good result against Bayer. We need the points desperately and I would obviously love to play my part in it."