The 30-year-old Dane was released by Leeds at the end of last season, and is expected to go straight into the side to face Swindon on Saturday.
Albion manager Gus Poyet said: "With Peter Brezovan injured, we wanted to bring some experience to that position. I have worked with him at Leeds United, and know exactly what he is capable of." He added: "He also knows what it takes to get promoted from League One."