BOSTON — A 79-year-old man who once supervised altar boys as a layman at a Catholic church in Boston has pleaded not guilty to charges that he sexually abused a young boy decades ago.

Michael Walsh was arraigned Wednesday on two counts of child rape and three counts of indecent assault and battery on a child under age 14.

Prosecutors allege Walsh abused a boy from the fourth- to sixth-grades between September 1988 and June 1991. The alleged victim is now 38.

Prosecutors say Walsh used his role at St. Brendan Parish in the city’s Dorchester neighborhood and his position as a youth baseball coach to “gain access to, groom and ultimately sexually assault the victim.”

Walsh was released with GPS monitoring. He and his lawyer refused to comment outside of court.