City have taken a 22-man squad to Germany for the first leg at the Red Bull Arena, which kicks off at 20:00 (UK).
Kevin De Bruyne and Aymeric Laporte, who started Saturday’s match at Nottingham Forest, did not travel with the squad along with John Stones who has not played since the FA Cup win over Arsenal in January.
And Guardiola revealed that De Bruyne and Laporte are both missing due to illness after feeling unwell following the 1-1 draw at Forest.
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“Kevin and Laporte [are missing through] illness,” the boss said in his prematch press conference. “They are not ready for tomorrow.
“It is what it is. During the season, unfortunately sometimes that happens.
““He (De Bruyne) didn’t feel good right after the game against Nottingham. Yesterday Aymer didn’t feel well.
“Other players are going to play. That happens sometimes.”
Guardiola is expecting a tough game against Leipzig who have been beaten just once in their last 20 games in all competitions.
They also won their last four games in the Champions League group stages to qualify for the last-16 including a win over holders Real Madrid.
“Right after the draw I knew it, I felt it would be a really tough opponent,” Guardiola said.
“We know the quality of them for many years. A culture for young players, recruitment, clear patterns of play, a lot of play in the middle, physicality in German football in the transition they are unstoppable. Many respects for this Club and what they’ve done.
“Last year with [former boss] Jesse Marsch and [Christopher] Nkunku we struggled. Here we lost - okay we had qualified - but we struggled.
“Every season they’ve qualified for the Champions League I know the quality and it will be a tough, tough two games.
“[We must] try to make a good performance, control our emotions and get a good result for the second leg in Manchester.”
