Both players were dropped entirely for last Saturday's 3-2 win at Fulham, Sage's first victory in charge, after the head coach was unimpressed with their performances as substitutes in the previous week's 4-1 home defeat by Manchester City.
Guessand had also been left out of Palace's Europa League squad in the same period. McNeil, on loan from Everton, appears to have taken the message on board, earning 15 minutes in Tuesday's Carabao Cup win over Middlesbrough. Guessand, on loan from Aston Villa for a second spell at Selhurst Park, has yet to respond in the same way.
"He hasn't responded at the level I expect," Sage said with a deep sigh ahead of Saturday's game against Ipswich Town. "He mentioned he was injured at the end of the warm-up for the game on Tuesday, that's why he didn't go on the pitch. I have to speak to him because we need to find a solution. We need to see the best version of him.
"I watched him in France for Nice and Nantes and he's able to do more than he's given us which is why I am really demanding of him. Sometimes it takes time but at the end everybody will win."
Sage was more encouraged by McNeil's reaction to being left out.
"Dwight's 15 minutes on Tuesday were much better than the minutes against Manchester City and in every session he showed us that he wanted to play. That's a good message and I have received his message," he said.
The Palace boss also addressed Adam Wharton's underwhelming start to the season, insisting the midfielder's high standards mean he holds him to an even higher bar than most of his teammates.
"My main objective with him is to get him a step higher than he is today. That's why maybe he is in a period where things are not stable," Sage said. "I had a good conversation with him in pre-season where I set his objectives really high and will push him to reach them.
"I'm really confident because he's a smart player, he understands the play and the importance of training well every day. He is in the learning process. Everybody knows him as a wonderful player but he can be more than wonderful. There's a gap in his potential and he can play better than he has played. He played really good but he can become recognised all over the world."