Bremen swoop for Wolfsburg's Casteels
The Belgian only moved to Wolfsburg on a permanent transfer from fellow Bundesliga side Hoffenheim on Wednesday.
Casteels has subsequently been allowed to join Bremen on a temporary basis until the end of the season and is likely to provide competition for regular number one Raphael Wolf.
"We made the decision together to sign Koen Casteels," Bremen head coach Viktor Skripnik told the club's official website.
"He will integrate very well here and it's a role he's highly motivated to accept."
Casteels made 39 Bundesliga appearances for Hoffenheim, but has not played since April due to a broken leg, an injury that kept him out of contention for last year's World Cup.