Barca have been heavily linked with the 22 year-old over the last few weeks and the Catalan club now look set to beat the likes of Manchester United and Manchester City to the winger's signature.
"Right now Barcelona just have to iron out a few details, but it's practically done," Quique Pina told Cadena COPE.
"It's 80% done and the other 20% is what's to be ironed out."
Pina revealed the fee will be around 45 million euros, although that is likely to include Barca's Spain Under-21 forward Jeffren Suarez.
"It's a figure close to 45 million, which is an initial value, including a player and other variables," he said.
Sanchez is reported to be leaving Chile's Copa America training camp to fly to Barcelona on Tuesday for a medical.
Source: Team Talk
Source: Team Talk