Aas started his career in
Moss FK in 1973. In 1976, they were promoted to the
Norwegian Premier League, and
Verdens Gang named him
central defender of the year in 1977 and 1979. His professional career started at
Bayern Munich, where he stayed for the 1979–80 season. Midway through the following season, he was transferred to
Nottingham Forest, at the time managed by
Brian Clough. A broken leg put a premature end to his stay at the City Ground. He returned to Moss in 1984, and helped the club win its first and to date only League title in 1987, before retiring as a player. ==International career==