The Aston Villa striker was not included in the squad to face Malta on Sunday, despite Celtic's Leigh Griffiths pulling out with injury.
Warnock, who managed McCormack at Leeds United, has sympathy for both the player and head coach Gordon Strachan.
"It was very difficult to find a system to suit Ross McCormack," said Warnock.
"I couldn't play him up front because he wasn't big enough or good enough in the air.
"I couldn't play him wide because I've got better wingers like Robert Snodgrass.
"So the only role I could give him really was in the hole like a number 10 behind the striker.
"You end up trying to find a system for one player and you can't do that."
McCormack signed for Aston Villa for £12m in August after scoring 23 goals for Fulham last season.
He made appearances for Scotland in friendlies against the Czech Republic in March then Italy in May but has been largely ignored by Scotland since making his debut in 2008.
"There's no doubt in my mind that Ross will score 20 goals this year in the Championship," Warnock told BBC Scotland's Sportsound. "He scores 20 goals every year.
"But it's very difficult to get a winning formula with him as he is - unless you give him that free role.
"He tried his hardest. He played wide left for me at times. He couldn't go past a player, but he would come in. He's good on free kicks and scores goals."
However, Warnock thought McCormack could warrant a place in the Scotland squad.
"You could always do with a Ross involved, which is why I'm surprised he's not involved," he added.
"If you are going to need a goal against a team like Malta, Ross can always give you that little bit different and create a chance.
"But you can't just pick him to be on the bench, so it is a dilemma.
"There's nothing wrong with the lad, he's a hard worker."
Neil Warnock believes Ross McCormack has not been called up to the Scotland squad because it is difficult to fit the striker into a winning system.