McDonald produced a clinical finish 12 minutes from time to cancel out Sam Winnall's opener at the Pirelli Stadium.
The point leaves the Gills in fifth place and Hessenthaler was a relieved man, as he was mulling over replacing McDonald.
The Gills boss said: "In a sense it was a missed opportunity for us because other results have gone quite well for us, and it would have been a great time to pick up three points.
"I haven't told him yet, but I was thinking about taking Cody (McDonald) off because he was quiet during the game.
"But you think twice when you've got as player with his scoring record and his goal for the equaliser was absolutely first class."
Source: PA
Source: PA