Mendy continues to struggle after undergoing knee surgery in November, despite making his comeback in the 1-0 win at Burton Albion in the Carabao Cup.
And Kompany's last appearance came in the victory over Liverpool at the tun of the year, a game that saw him pick up a muscle injury.
Barring long-term absentee Claudio Bravo, the the rest of the squad are fit, and Guardiola promised to respect the League Two side by naming a strong starting lineup.
"They [Mendy and Kompany] are not ready for tomorrow,” Guardiola told journalists.
“We are going to make a strong team. We have deep squad.
“The other ones are fit and a few players who haven’t been playing may play.
“We go game by game.”
One possible concern for Guardiola and his staff is the state of the pitch at Rodney Parade, which is also used by Newport RFC and the Dragons.
Newport's midweek defeat to MK Dons was the 60th match played this season by County or the rugby sides, meaning there are areas where very little grass is visible.
Indeed, in the second leg of their fourth-round tie with Middlesbrough, a game they won 2-0, the pitch cut up badly and made playing the ball along the ground very difficult.
But Guardiola says there is no point complaining and believes his players are well prepared fir such adversity.
“They play at home and can do whatever they want,” he said.
“I seen vintage games here in 70s and 80s and all the pitches were bad. Now, most of the pitches are perfect.
"You don’t win anything complaining about that. They own their stadium and can play how they want.
“All I can say myself, my players dreamed when they were young to play on pitches like this.
“When they were 15, 16, 17, they played on these kinds of pitches, and me too.”