Yatabare, 26, has cost Werder 2.5 million euros ($2.72m) and having made 18 international appearances for Mali, the defensive midfielder has signed a contract with Bremen until June 2019.

"Sambou is tall, powerful, dynamic and courageous, but like any new player he will need time to adjust," said Bremen's director of sport Thomas Eichin.

"He is a player both the coach and I wanted to sign. He was number one on our list and we are pleased the transfer has come off."

Bremen, who are third from bottom, host third-placed Hertha Berlin in Germany's top flight on Saturday, which comes too soon for Yatabare to feature.

Tremmel, 37, was born in Munich and boasts 125 Bundesliga appearances with SpVgg Unterhaching (in 2000/01), Hannover 96, Hertha Berlin and Energie Cottbus.

He has been brought in as cover for first-choice shot-stopper Felix Wiedwald, with reserve goalkeepers Michael Zetterer and Raphael Wolf struggling with injuries.

"We needed to reinforce in goal," explained Eichin.

"Gerhard Tremmel is a goalkeeper with a huge amount of experience who will support our young goalkeepers and Felix Wiedwald."

Meanwhile, Bremen has sent Germany star Toni Kroos' brother Felix, who made eight league appearances this season, on loan to Berlin-based FC Union, who are mid-table in the second division.

The Bundesliga's winter transfer window closes at 1800 local time (1700 GMT) on February 1.