Herrera is currently on national team duty representing the U-23 side that has already made history at the Toulon Tournament, while Bueno won the U-17 World Cup in 2011
The Anfield outfit were previously the only side to express an interest in both players, according to the Mexican team's officials, but the Red Devils are now also tracking the two youngsters.
"It's not just Liverpool. Manchester United are also after Marco and Hector," said Jesus Martinez Patino to Raza Deportiva.
"However, we're of the thinking that they must first consolidate themselves in Mexico," the chairman added.
Herrera, the oldest of the pair at 22, is currently with the Mexico U-23 contingent in Toulon that will play the prestigious French tournament's final on June 1. The central midfielder was also signalled as one of El Tri's key players during the pre-Olympic qualifying tournament that secured a spot in London 2012.
Bueno starred for Mexico's U-17 team last year when the North Americans won the World Cup at home, beating Uruguay 2-0 at the Estadio Azteca. After the tournament, Liverpool took him on trial for a period over the summer.