Valencia's fellow Ecuadorian collapsed and died of heart failure in July, aged just 27.
The news shook an entire nation, including Valencia, who has also had a tattoo on his arm in tribute to Benitez.
"It is terrible that he passed away," Valencia told MUTV.
"He wasn't just a friend but a brother to me.
"I dedicated the tattoo and the goal celebration, and hopefully every other goal celebration, to him.
"We all loved him and it had a huge effect on the whole country.
"He was a top guy. He was humble and worked very hard to provide for him family. He was good fun to be around.
"It was unbelievable news to hear that at 27, he is going about life normally, then the next thing you see is that he has passed away."
After scoring just once last season, Valencia has been challenged to get "seven or eight" by manager David Moyes, which would represented his highest total since joining United in 2009.
"I actually said to him 'you should be getting yourself seven or eight goals a season regularly'," said Moyes.
"Antonio looked at me and squinted a bit.
"He only scored one last season but he's got off to a good start and hopefully he'll get close to the target I'd like to him get this year."
The former Wigan man feels he has a better chance of achieving that feat wearing the 25 shirt, which he has reverted back to after passing up the coveted number seven jersey in the summer.
"It is something I have been considering for a while," said Valencia.
"Maybe it is psychological or just a good luck symbol. In Ecuador we have things that bring us good luck.
"It turned out to be a very good number for me when I first arrived at the club.
"Hopefully I can regain the form I showed before."