The Grangetown-born striker, 21, scored seven times for the National League North side in a short loan spell there a year ago.

O'Neill was recalled by Boro's then head coach Jonathan Woodgate and made his senior debut for the club as a substitute at Elland Road.

The Academy man, who also had a stint on loan with Hartlepool United, returns to Darlington until January, where he will be managed by former Boro forward Alun Armstrong.