Arsenal have activated the Spain forward’s £17.1m release clause, forcing Deportivo to sell.
He too has passed his medical after flying into London last week.
The 27-year-old will host a press conference today to say goodbye to the Deportvo fans.
Mustafi, meanwhile, revealed yesterday how Germany team-mate Mesut Ozil helped convince him to join.
He said: “I did not see Per for a long time because he quit international football but I talked to Mesut.
“He told me everything I wanted to know. Everything was positive, so I was convinced very fast. It did not take much.
“I have always loved Arsenal, I like how they play here, it is not typical English.