The 21-year-old right-back is reported to have visited Rotterdam to check out Feyenoord's stadium and facilities.
Chris Woerts, a director of the club said: "The player was deeply impressed by the stadium. He looked around the locker rooms and visited the city."
"He has spoken with coach Erwin Koeman, who came back to Rotterdam from his holiday home specially to meet him."
Johnson was signed from West Ham United for £6m in 2003 but rarely used last season by Jose Mourinho.