Donny Isaak (born June 10, 1969) is an American former professional tennis player.

Isaak, a native of Carroll, Iowa, played collegiate tennis for the University of Southern California.

He was a member of USC's 1991 NCAA championship team, as well as an NCAA singles semi-finalist and All-American that year.

[1] In the early 1990s he competed on the professional tour and reached a best singles world ranking of 288.

He made a doubles main draw appearance at Indian Wells in 1991, partnering Swede David Ekerot.