Five-weight world champion Pacquiao won a seat in the Philippine Congress in May and Roach said there are signs he has fallen out of love with the sport.
Pacquiao, 31, meets Antonio Margarito for the vacant WBC light-middleweight crown in Dallas on 13 November.
"We are going to lose Manny Pacquiao to politics, for sure," Roach told BBC World Service.
"After the first couple of days of training Manny came up to me and said 'I miss my job', and I said 'you're at your job', and he said 'no, I miss Congress'."
Pacquiao, who is a national hero in the Philippines, represents the province of Sarangani and stated after being elected that he would have only one more fight.
We're fighting against a big, strong guy and we haven't had the best training camp
Freddie Roach
And Roach's comments will disappoint boxing fans across the globe because they suggest a super-fight with American great Floyd Mayweather will never happen.
A planned fight between the pair fell through in January when Pacquiao refused Mayweather's demands for random blood and urine tests.
And Roach added he was concerned by Pacquiao's preparation for the Margarito contest, saying they "haven't had the best training camp".
"I'm worried about the fight a little bit," said Roach, who was talking to BBC boxing commentator Mike Costello in the Philippine city of Baguio, where Pacquiao has been sparring with, among others, Britain's WBA light-welterweight champion Amir Khan.
"We're fighting against a big, strong guy who's going to be in great shape and we're a little behind schedule which is very unusual.
"I'm not sure if it's the size of the sparring partners that's giving him trouble or he's just not himself yet.
"He's getting better and better every day but it's coming a lot slower than usual.
"Usually Manny has his first sparring session and could fight 12 rounds the next day, I can't say that at this point in the camp.
"But we do have two hard weeks of sparring coming up before we start tapering off and slowing down and saving it for the fight."
As well as boxing and politics, Pacquiao has appeared in feature films, television shows and released a number of albums.
Mexico's Margarito, a former welterweight world champion, has won 38 of his 45 fights and has fought some of the biggest names of the era.
However, he was banned after illegal hand wraps were found in his gloves before a bout against Shane Mosley last January and has fought only once since then.
Could this be a ruse by Freddie to lul Marg into a false sense of security? Or is Manny really falling out with our beautiful game?
Would be a massive loss for boxing especially the fight all fans want to see....Mayweather
Thoughts??
Cheers SLH
