De la Hoya (left) and Pacquiao meet at the MGM Grand in Las Vegas
Freddie Roach has called former charge Oscar de la Hoya a "part-time fighter" ahead of the American's super-fight with Manny Pacquiao on 6 December.
Roach will be in Filipino superstar Pacquiao's corner in Las Vegas.
"Oscar is 35 and it's obvious Father Time is catching up with him," said Roach, who also trains Amir Khan.
"Boxing is a young man's game. Oscar is going to find out how [Mexican legend] Julio Cesar Chavez felt the night he lost to Oscar the first time."
Six-weight world champion De la Hoya inflicted only Chavez's second defeat in 99 professional fights as a 23 year-old in 1996.
A gold medallist at the 1992 Olympics, De la Hoya has since gone on to become the most marketable name in boxing, amassing a record of 39 wins and five defeats.
The career cycle of any athlete is finite. It's dangerous to overstay your welcome
However, he has lost three of his last six fights and has only fought three times in the last four years.
The 29-year-old Pacquiao, meanwhile, is a former flyweight world champion and arguably the finest pound-for-pound boxer in the world today.
But the former four-weight world champion has never fought higher than lightweight before, leading many to believe he has little chance against De la Hoya.
The clash at the MGM Grand will take place at welterweight, but Roach believes size will be no obstacle to his charge.
"Manny can flat-out fight three minutes of every round for 12 rounds and he picks up a new lesson the first time it's shown to him," said Roach.
"Manny not only has the discipline and the stamina to follow a script in the ring, he has also become a master at improvising. And I think that may be the difference in this fight.
"Oscar works well when he can follow a script, but he showed in his fight against [Floyd] Mayweather [De la Hoya lost on points last May] that he's even having problems doing that.
"Our game plan was working well the first half of the fight and then he stopped.
"The career cycle of any athlete is finite. Good habits and good genes can postpone the erosion of an athlete's talents, but eventually the inevitable catches up with even the best of them. It's dangerous to overstay your welcome.
"You don't have to look any further than these four examples: Rocky Marciano ending Joe Louis' career, Larry Holmes ending Muhammad Ali's career, Terry Norris ending Sugar Ray Leonard's career and Oscar de la Hoya ending Julio Cesar Chavez's career.
"Next week, the shoe is gong to be on the other foot for Oscar."
Manchester's Ricky Hatton hopes to fight the winner of the fight next summer, possibly at Wembley Stadium.