Hill, a seven-year veteran, is batting just .225 with six home runs and 45 RBI in 104 games. His best season came in 2009, when he clubbed 36 homers and 108 RBI with a .286 batting average.
The 13th overall pick of the 2003 draft by Toronto, he is a career .265 hitter with 96 homers and 409 RBI in 875 games.
McDonald has appeared in 65 games with the Blue Jays this season and is batting .250 with two homers and 20 RBI.
A 13-year veteran, he has hit .240 with 21 home runs and 177 RBI in 865 career games with Cleveland, Detroit and Toronto.
Johnson has batted just .209 with 18 home runs and 49 RBI in 114 games this season.
Selected in the first round of the 2000 draft by Atlanta, he is a .260 hitter with 89 homers and 326 RBI in 758 games with the Braves and Diamondbacks.
In a related move, the Diamondbacks also transferred pitcher Jason Marquis to the 60-day disabled list. He was originally placed on the DL August 16 with a fractured right fibula.