The New Normal actress Brighton Sharbino will play a 10-year-old version of the tech whiz in a February episode of the CBS procedural, TVLine reports.
"Rather than look back at her first days of working at NCIS, I was more interested in, 'When did Abby first start to develop an interest in forensics? And in people? In bodies, and in clues?' Things like that. So we decided to go way back," showrunner Gary Glasberg explained.
Child actress Sharbino has previously appeared in episodes of Hannah Montana and NBC's Prime Suspect remake, launching her career in 2008 with a minor role on Friday Night Lights.
NCIS continues to be one of CBS's best-rated shows, with a recent episode attracting 19.57m viewers.
CBS is currently developing a new series based on the NCIS franchise. The show - which would follow a team of crime-busting agents who both work and live together - would be spun off from NCIS: LA.
NCIS continues on Tuesdays at 8/7c on CBS. In the UK, the show airs on FX, as well as CBS Action, Channel 5 and 5USA.
> NCIS casts Star Wars actor Billy Dee Williams as a war veteran
Watch NCIS star Rocky Carroll's recent interview with Digital Spy below: