Winger fit ahead of return to former club.
Gavin has been absent since the away defeat at Shrewsbury Town, but is now back in the fold for the weekend's First Round tie.
His return to fitness will see him return to the club where he spent time on loan during his stint with Watford.
Fellow forward Marvin Sordell will also be making a return to Grosvenor Vale on Saturday, having also been out on loan there from the Hornets.
The U's will wait on the fitness of Jamie Jones, who has been struggling with a hamstring injury, but fellow loanee Callum Harriott will be available after permissions to play in cup competitions was built into his loan deal when he arrived from Charlton.
The game kicks off at 3pm.