Nilsen played for Norwegian club Skiens Grane before moving to the United States in 1923.

The onset of the Great Depression in 1929, combined with the costs imposed by the "Soccer Wars" between the ASL and United States Football Association (USFA) led to severe financial problems with the league and its teams.

While the league standings reflect the Yankee name, the team won the 1931 National Challenge Cup under the Fall River F.C.

As in 1928, Nilsen joined a collection of U.S.-based Scandinavian players in 1931 to make a tour of that region, this time as part of Brooklyn Gjoa.

To make matters more confusing, in summer of 1931 the Yankees moved to New Bedford, Massachusetts, merged with Fall River F.C.

Despite the turmoil, Nilsen and his teammates added another "double" to their resumes as they took both the 1932 league title and the National Challenge Cup.

After the games, Whaler's Scottish international Alex McNab decided to join Stix as a player/coach for the 1932–33 season.

Nilsen remained with Central Breweries which won the 1934–35 league championship, but did not participate in the team's 1935 Challenge Cup victory due to injury.

In 1934, Nilsen earned two caps with the United States when he was selected to the 1934 FIFA World Cup roster.

[3] According to the Soccer Hall of Fame, Nilsen worked as a machinist and a men's clothing model in both Boston and St. Louis.

The National Soccer Hall of Fame inducted Nilsen in 2005 as part of a process of recognizing significant pre-1950s players.

In order to correct these oversights we established a Blue Ribbon panel consisting of historians Colin Jose, Roger Allaway and Hall of Famer Walter Bahr, to review the credentials of all Veterans from the pre-NASL era.