Oli, who missed three months of last season with a foot injury, was forced off after just 17 minutes of the clash following a heavy challenge on the edge of the area, and his injury will be assessed when the club return to England from their trip to France.
Manager Mark Stimson is already preparing to start the season without midfield pair Stuart Lewis and Adam Miller, who both missed the trip across the Channel after suffering injuries in the 3-1 win at Bishop's Stortford on Tuesday night.
The game itself was a competitive pre-season encounter which saw four players booked in a fiery second half, but the closest either team came to scoring was when Heredia Mayombo hit the post for the home side.
Meanwhile, former Gills midfielder Nicky Southall - released at the end of last season - has joined Conference South new-boys Dover.
The 37-year-old made almost 400 appearances in three spells with the Kent club and has now linked up with ex-Gills boss Andy Hessenthaler at Crabble, where he had a loan spell last season.