The 23-year-old has been strongly linke with a summer move to Manchester United.
Reports claim Jose Mourinho would be keen on signing the striker, if he is named as new United manager.
But Thohir insists the striker will remain at the San Siro.
“Icardi stays because he’s a part of a plan, so too are Jeison Murillo, Miranda, Gary Medel and Geoffrey Kondogbia,” Thohir told Sky Spot Italia.
“We want to build a group for 2-3 years. We can’t change the team each season.”