A band director with the Fairfax County schools has been placed on administrative leave after he was charged with soliciting a 15-year-old online, authorities said Monday.

Fairfax County police said Michael K. Cook, 43, of Centreville was arrested Aug. 31. He works at Robinson Secondary School in Fairfax, which has more than 4,000 students in grades seven through 12.

Police said in a statement that the alleged victim “was not a student at the school or anyone under the arrestee’s supervision.” No further information about the alleged incident was available from police. Police spokeswoman Lucy Caldwell said police did not announce the arrest earlier because they did not want to jeopardize their investigation.

Fairfax students return to class from summer vacation Tuesday, and the Robinson Marching Rams band, which has been practicing for weeks, will enter the busy fall season without Cook, the program director. Paul Regnier, spokesman for the Fairfax school system, said that Cook was placed on unpaid administrative leave and that the school will conduct an internal investigation.

At Robinson, Cook’s responsibilities included directing the symphonic band and the Marching Rams. He has led student performance tours to Western Europe, and he plays the tuba in the Fairfax Wind Symphony, according to his biography. Robinson Principal Dan Meier planned to e-mail all parents Monday night about the arrest and tell them about arrangements for a substitute band director, Regnier said.

According to the school’s band Web site, Cook graduated from the University of Maine in 1990 with a degree in music education. He taught middle and high school instrumental music in Maine for eight years before moving to Virginia. He earned his master’s degree at George Mason University in instrumental conducting in 2001.

Cook is being held at the Adult Detention Center and is scheduled to appear at a 10 a.m. hearing Tuesday in Fairfax District Court.