Grella has still to score for Leeds in a senior match, although he did score in the pre-season friendly at Burnley.
He said: "I'm absolutely delighted to have signed the deal. It is good to know that the club have instilled a bit of belief and confidence in me. I want to be part of the group and play as big a part as I possibly can in getting Leeds promoted so we'll have to wait to see how it plays out."