The newly promoted La Liga side will host Barcelona on Saturday from 9.45pm in a match that they must to win to move up the table.
Olunga joined Girona in August and has made one appearance, coming in as a second half substitute for his side in a 1-0 defeat to Sevilla last week.
The former Djurgadens IF striker, who is on loan from Chinese Super League side, Guizhou Hengfeng Zhicheng, is expected to line-up against world best player, Messi tonight.
Barcelona are top of La Liga table with 15 points while Girona are sitting a distant 15th with only five points after five rounds of matches.
Barcelona will be without Ousmane Dembele, who is unlikely to play again this year, as well as Rafinha while midfielder, Andres Iniesta could be rested.
Olunga is the second Kenyan after McDonald Mariga to have played in the La Liga.