Fernandes is reportedly nearing a switch to struggling Premier League giant United, with a fee in the region of £51million (€60m) being mooted, though Sporting is believed to be holding out for more.
After confirming Fernandes will face Portuguese rival Benfica ion Saturday, Silas hailed the Sporting captain.
"He is an extraordinary player, the best and most valuable in the league, as he was last season," Silas said. "I've heard someone say that he's not worth the money you are talking about and it's true, he's worth a lot more.
"In addition to attacking he also sacrifices himself to defend. Bruno is the best and the most valuable. When we have such a player it's normal for everyone to want him."
Fernandes, who was heavily linked to United, Tottenham and Real Madrid during the previous transfer window, has scored 15 goals across all competitions for Sporting this season.
The 25 year-old midfielder netted 31 goals last season, including 20 in the Primeira Liga.