The Robins lost the first-leg 2-1 on Tuesday night despite taking the lead through Reid's penalty conversion.
Speaking after the game, Reid said: "Very disappointing. We are still in the game and our fans will be right behind us at Ashton Gate. We gave it our all and just came up short.
"We beat Manchester United and we have a chance. We have to take it to them. It gives us great confidence going a goal ahead and holding on for so long."