Gray is hopeful that one of his players can make the most of their chance in Doig's absence.
"We just have to get on with it and one man's loss is another's gain," Gray told the club's official website.
Striker Adebayo Akinfenwa will be on the sidelines alongside Doig as he serves the second match of his four-match ban for his dismissal in the 1-1 draw with the Seagulls.
The Cobblers are also still without midfield duo Liam Davis (hernia) and Luke Guttridge (knee).
MK Dons boss Roberto Di Matteo has the luxury of choosing from virtually a fully-fit squad.
Midfielder Luke Howell has returned to full training after missing the last month with a hamstring injury and could be included at Sixfields.
Fellow midfielder Luke Chadwick played 72 minutes of the 2-2 draw with Leicester at the weekend following a hamstring injury, but came through the match unscathed and is expected to keep his place in the side.
Defender Sean O'Hanlon returned at back against Leicester after a month out with a hip problem and played all 90 minutes and will keep his place.
Fellow defender Danny Swailes remains a long-term absentee with his Achilles injury.
Sporting Life