A dominant player through the 1930s and a member of the U.S. national team at the 1934 FIFA World Cup, McLean disappeared without a trace in 1938.

His disappearance remained a mystery until June 2022, when an investigation by The Athletic's Pablo Maurer and Matt Pentz uncovered the details behind that disappearance; McLean had suffered a nervous breakdown after multiple head injuries and lived out the last 40 years of his life in a series of public mental health facilities.

continued the success they had experienced under the old name by winning a third Challenge Cup and league title in 1935, giving McLean three "doubles" in three years.

[2] While recovering from his 1936 collapse, McLean was called up to the national team for a three-game series with Mexico in 1937, but did not play.

For years, it was assumed that McLean had died; in 1944, Aetna Life Insurance placed an ad in the Midwest Soccer News asking for information about his whereabouts.

In 2022, The Athletic's Pablo Maurer and Matt Pentz concluded a two-year-long investigation into McLean's mysterious disappearance.

In 1959, McLean was transferred to Pine Knoll Home in Davenport, a publicly-run assisted living facility, where he died on November 6, 1977.