The Serbian left-back will sign a one-year contract with the option of a second season at the San Siro.
34-year-old Kolarov has spent the last three years in Rome after arriving from Manchester City.
Vidal, 33, is open to a second Italian adventure after his time with Juventus and Barcelona want him to leave.
The Catalan club are trying to get a transfer fee for Vidal and that is the current sticking point.
Inter, knowing Barca want the Chilean’s salary off their books, want them to release Vidal for free.
A resolution is expected and unless of any major surprises Vidal will then sign a two-year deal with Antonio Conte’s side.