The 31-year-old has been told that he no longer has a future at Real Madrid and talk of a return to the Premier League has gathered pace in recent days.
Barnett has now said that his client is closing in on a switch to the Tottenham Hotspur Stadium, and United are not expected to make a late attempt to hijack the deal.
"It's close but not done. It's a complicated deal," Bale's agent told AFP.
The former Southampton youngster turned out for Spurs between 2007 and 2013, scoring 55 times in 203 appearances for the London giants before moving to the Spanish capital.