Crystal Palace secured a 3-2 win at Fulham at the weekend, Sage's first victory since succeeding Oliver Glasner, thanks to a Tyrick Mitchell brace and a Ben Chilwell winner, but did so without summer signings McNeil and Guessand in the squad entirely.
Neither absence was down to fitness; both players had come on as second-half substitutes in the previous week's 4-1 home defeat to Manchester City without making an impact, and Sage opted to leave them out completely at Craven Cottage.
"It's my decision, a sporting decision," Sage said of the call, according to Sky Sports.
"Sometimes players have to be shaken to come back and regain their level. In the end, it's only one game.
"With a few games, everybody gets excited about the situation — what's happened, is there a problem, or something like this. That's how it is. They need to take this information and use it to change things in training, because they have the chance to show themselves every single week."
Sage has been in charge for only a handful of matches since replacing Glasner.
McNeil arrived from Everton over the summer, while Guessand has returned to Selhurst Park on a fresh loan from Aston Villa having spent time there previously, and both were expected to feature prominently in Palace's attack this season.
Their omission came just days after Guessand was also left out of Palace's registered squad for the Europa League, a decision that had already prompted questions over his role under the new head coach.
Sage left the door open for a swift recall for both players when Palace host Championship side Middlesbrough in the Carabao Cup third round on Tuesday.
"Maybe they're back with us on Tuesday," he said.
The win at Fulham lifted Palace to 13th in the Premier League, their first points of the season after opening defeats to Everton and Manchester City, and offered an early sign of the standards Sage intends to set as he looks to stamp his own identity on the squad he inherited.