The 19-year-old has made 11 senior appearances for the club since turning professional last summer and has been tipped as star of the future.
"We've got high hopes for Zac. He is a young lad who will have to go out on loan and get some games and see how the real world is," Leeds boss Neil Warnock told the club's official website.
"He's had a taste of the first team at the end of last season, now we need to get some games lower down and some experience. I always remember when I first signed Paddy Kenny I loaned him to Whitby Town and it makes you a bit more aware of the situation.
"We've got every faith in Zac that's why we offered him the contract. With Green coming back after the international break and Norris back now, this is a good time for Zac to get some games."
Thompson captained the club's reserve team last season.