"Politic should think about it carefully. Manny, I think Manny is entertaining, well it's good... Getting tired is the only thing you get from this work," Duterte said on Monday night at an event.
The boxer, who has been in the Senate since 2016 and whose possible candidacy for the presidency looks to be increasingly strong, was also one of the guests at the event, Efe news reported.
Pacquiao is the only fighter in the history of boxing who has won 12 major world titles in eight different weight categories.
He is one of the Philippines' most internationally known figures and many in the country consider him a national hero.
Duterte also reiterated his opposition to his daughter Sara Duterte, the current mayor of Davao, running for president in the 2022 elections. She is also favoured to take over from the 74-year-old leader.
"Were it not for the love of country, that's the only thing that sustains me. You would not get anything from this job except work and worry, and be under stress," said Duterte, who added he doesn't want his daughter to suffer the same.
In the legislative and municipal elections in May, Sara Duterte, 40, won a landslide victory her position as mayor of Davao - a post her father held for two decades intermittently - and as a leader of a regional political party platform, she gained nationwide visibility.
Several politic highlighted her charisma and announced their support for the president's daughter if she moved into Malacanang Palace, although she has stated on several occasions that she doesn't intend to.
( With inputs from IANS )