Alonso spent six seasons in the North American Soccer League, four in Major Indoor Soccer League, at least three in the American Indoor Soccer Association, one in the American Soccer League and two in the American Professional Soccer League. NASL
Alonso played the 1983-1984 NASL indoor season with the Chicago Sting. Advanced Systems Limited/APSL
Following the collapse of the NASL following the 1984 season, Alonso spent several seasons playing indoor soccer.
He returned to the outdoor game in 1989 with the Fort Lauderdale Strikers of the American Soccer League.
That year he led the league in scoring with ten goals and seven assists. He was also named a first team All Star.
In 1990, the Advanced Systems Limited merged with the Western Soccer League to form the American Professional Soccer League. Alonso remained with the Strikers, now in the APSL. In 1991, he then moved to the Miami Freedom for the 1991 season before retiring.
MISL
The year before that, the Chicago Sting entered the 1982-1983 Major Indoor Soccer League season.
With the collapse of the NASL in 1984, Alonso became a dedicated indoor player. He signed with the Minnesota Strikers for the 1984-1985 season. When he was released by the Strikers, he returned to the Sting, which was now competing in MISL. On October 24, 1985, he signed a one-year contract with the Sting after a month-long trial.
On April 29, 1986, he signed another one-year contract with the Chicago Sting of MISL. That year, he moved to defender.
AISA
The Sting released Alonso after a disappointing 1986-1987 season and he signed with the Jacksonville Generals of the American Indoor Soccer Association for the 1987-1988 season. He then moved to the Memphis Storm for the 1988-1989 season, however, he was traded to the Fort Wayne Flames during the season.
Alonso then spent the 1989-1990 season with the Memphis Rogues.