RB Leipzig's sporting director Ralf Rangnick is taking over as coach again while the club wait for Hoffenheim's Julian Nagelsmann to join in 2019.
American Jesse Marsch, who left his post with the New York Red Bulls on Friday and had been linked to the head coaching job, will instead serve as an assistant alongside Leipzig's under-19 coach Robert Klauss.
"It came down to carrying responsibility. I know the league, the team and I speak the language," Rangnick said. "That isn't the case yet for Jesse Marsch, so that's why he will be working as an assistant coach."
Rangnick previously led the team in season 2015-16, leading them to promotion before Ralph Hasenhuttl took over ahead of their Bundesliga debut.
Hasenhuttl quit in May after failing to agree a contract extension. Hoffenheim announced last month that Nagelsmann, the German coach of the year for 2016, was to replace him after one more season at Hoffenheim.
Leipzig have made three new young signings for next season -- 20-year-old French defender Nordi Mukiele for a reported €16 million from Montpellier, Uruguayan defender Marcelo Saracchi, 20, for a reported €11m from River Plate, and 19-year-old Brazilian forward Matheus Cunha for a reported €15m from Swiss side FC Sion.
Rangnick said the club would look to make three more buys as they prepare to improve on their sixth-place Bundesliga finish from last year, and a campaign in the Europa League.
Marsch, a former U.S. international, has long pursued the chance the coach in Europe and left the New York Red Bulls briefly in the 2017 preseason and again last summer to work towards his UEFA Pro License.
Both clubs are owned by the Austrain energy drink company Red Bull.