Hernandez joined United after the 2010 World Cup, with the transfer having been agreed before the tournament, but kept under wraps, with Hernandez and his father being the only non-representatives aware of the deal.
In his five years in Manchester, Hernandez made 157 appearances and got on the scoresheet 59 times.
He spent last season on loan to Spanish giants Real Madrid after he fell out of favour with new boss Louis van Gaal. He scored nine times in 33 outings with Madrid.
Liverpool wanted to sign the striker this month, says Smith, but the German club had no interest in parting ways with the 27-year-old.