The 29-year-old former Barcelona and Juventus defender signed a short-term deal with the Premier League club last week and impressed Puel during a training camp in Spain.
Southampton are trying to win their first silverware since beating United in the 1976 FA Cup final.
"It's a good surprise about Martín, because he is physically fit and we will see if he can participate for the final," Puel told reporters.
"It would be his first game in one year, but I think he can give a good solution - perhaps for the final, and for the future."
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Caceres, who played for Uruguay in the 2014 World Cup in Brazil, has been without a club since his contract with Juventus ended last June.
Puel is also hoping to be able to select Moroccan midfielder Sofiane Boufal after he returned to training following an injury that kept him out of Southampton's last game, a 4-0 Premier League hammering of Sunderland.
"Sofiane comes back step-by-step in the training sessions," Puel said. "We will see tomorrow. He is better and I hope he can participate also with the squad."
(Reporting by Martyn Herman, editing by Ed Osmond)
