Kearney has been in superb form this season, starring for club and country and earning a place in Ian McGeechan's Lions squad that leaves for South Africa on Sunday evening.
The 23-year-old full back / wing contracted Mumps at the end of April and has only appeared once since then.
He was fit enough to start against the Dragons in the Magners League last week but Cheika has decided to stick with the same back three that helped crush Munster in the Heineken Cup semi-final at Croke Park on May 2.
"We just feel that he needs a little bit more before he starts a game," said Cheika after he named Isa Nacewa, Shane Horgan and another 2009 Lion Luke Fitzgerald in his starting line up.
"Rob's obviously going to play a part in the game in some stage. We just felt that he needed to have a little bit more running behind him.
"I think we may have taken something from our experience when Shane Horgan was actually ill earlier in the season. Maybe we brought Shane back to the top level a bit too soon.
"Rob understands that he's going to have a role to play in the team, it's just a matter of at what stage in the game his does that."
Although Kearney has to make do with a spot on the bench, Leinster still include three current Lions in their first-choice XV, with Jamie Heaslip, Brian O'Driscoll and Fitzgerald all starting in the Scottish capital.