Notre Dame defensive ends Stephon Tuitt and Aaron Lynch did not play in Saturday's 35-31 loss to Michigan.
And that had more to do with Wolverines quarterback Denard Robinson then the two freshmen, Diaco said.
"It was a little different preparation last week," Diaco said. "That was basically by design. A lot of that offense sets itself up option-ish. Where everybody's got to be in there fit and responsibility is as much of a factor in fitting plays as it is the physical attributes.
Tuitt and Lynch both played in the season opener against South Florida with Lynch assisting on a tackle for loss.
Diaco said the two newcomers will have larger roles in Saturday's home game against No. 15 Michigan State, which runs a pro-style offense with a quarterback in Kirk Cousins known more for his accuracy than his running ability.
"They're going to play a much larger role in the game this Saturday then they were going to last Saturday," Diaco said.