Professional career
After being drafted by the Seattle SuperSonics in the 1979 NBA draft he signed a contract with 3A Antonini Siena of the Italian Serie A.
Donaldson played three seasons with Seattle before moving on to the San Diego (later Los Angeles) Clippers. During the 1984–85 NBA season, he led the league in field goal percentage at 0.637—still one of the ten highest percentages in NBA history.
Donaldson cited Artis Gilmore, Darryl Dawkins, Moses Malone, Truck Robinson and Maurice Lucas as some of the strongest players he played against early in his career.
Donaldson joined the Dallas Mavericks in 1985. He joked with teammates that leaving the lowly, dysfunctional Clippers for the Mavericks was like dying and going to heaven. He had his finest years while playing for the Mavericks, providing rebounding and shot-blocking to complement Dallas' star-studded line-up, which included Mark Aguirre, Rolando Blackman, Roy Tarpley, Derek Harper, Sam Perkins, and Brad Davis. Donaldson himself earned a spot on the 1988 All-Star Team during a season in which the Mavericks reached the Western Conference Finals before losing to the Los Angeles Lakers. The NY Daily News named him the worst All-Star player ever after fan voting. Donaldson was eventually traded to the Knicks for Brian Quinnett.
In 1990 he was founder and CEO of a dating magazine named Eligibles. It was published for a brief period of time in Dallas-Ft. Worth before going out of business.
After brief stints with the New York Knicks (traded midway through 1991–92 for Brian Quinnett) and Utah Jazz (49 games in two seasons combined) in the early 1990s, injuries forced Donaldson into retirement from the NBA. He left the league in 1995, with 8,203 career points, 7,492 career rebounds and 1,267 career blocks. He played in 957 NBA games without ever attempting a 3-point shot, a record among players from the 3-point era.
On August 1, 1993, he signed for Greek Basket League club Iraklis. He played in 30 games for Iraklis averaging 12.1 points per game, 12.2 rebounds per game and 2.2 blocks per game. In the 1996–97 season he played for Caja San Fernando averaging 3.5 points and 3.6 rebounds per game. He also had spells with Snai Montecatini (Italy, 1997–98, for only six games), Breogán Lugo (Spain, two stints, in 1998 and 1999) and Gymnastikos S. Larissas (Greek Second Division, 1998–99), retiring for good at the age of 41.
