According to Goal's news, Liverpool will rent Carrius again because they failed to find a team willing to sign the German goalkeeper directly.
Karius was loaned to Besiktas by Liverpool in the past two seasons. Due to salary issues, the two sides cancelled the loan contract in advance.
Karius returned to Liverpool in May and he has no future in the team.
Liverpool had hoped to sell Carrius this summer to raise funds, but no team officially made an offer.
Karius will join the Berlin Union on loan, and he will undergo a medical examination on Monday local time.
Hertha Berlin and Montpellier have also been asking prices, but the Berlin Union will be the place for Karius.
Liverpool believes that Carrius is worth 6 million pounds, and the player's joint loan contract with Berlin will not contain any form of buyout clause.
Liverpool executives hope that Carius can regain his form in the Bundesliga, which can help them get better offers in the future.