City will come up against PSG's formidable forwards in the first leg in Paris on Wednesday and Guardiola said the pair are so good, they can give opposing managers restless nights.
"Always I believe the quality of these players, they have too much," Guardiola told a news conference on Tuesday. "I tried to sleep well last night and that was when I was not thinking of them. Incredible top players, their quality. We are ready to try to stop them, defend as a team, play good football and try to score goals."
After joining Barcelona in 2013, Neymar moved on to PSG in 2017 but Guardiola said there would be more Champions League trophies in the Camp Nou trophy cabinet had he stayed.
"I remember against Santos, I said this was the king of Santos and all the players were open mouthed: 'Oh my god, what a player,'" Guardiola added.
"A joy to watch as a spectator, he has Brazil on his shoulders, the No. 10, it's not easy to wear.
While the tie is only City's second Champions League semifinal, PSG are trying to reach for the final for the second year in a row after narrowly losing out to Bayern Munich last season.
Since then, Thomas Tuchel has been replaced as manager with Mauricio Pochettino.
The former Tottenham boss has been able to get the best out of Neymar since he arrived in January, leading to speculation the 29-year-old is a candidate for the Ballon d'Or and is set to extend his contract.
"I have already talked about it [his contract]," Neymar told a news conference on Tuesday.
"It is not a topic now. I feel great. I am happy this season. It has been by far my happiest this season.
"My main objective is the Champions League, not the Ballon d'Or. That is not a priority. I want to be a leader for my team. I want to win. In the future, I will want to remember I have managed to win the Champions League a few times."