Jean-Philippe Mateta was rushed to hospital after a heavy collision with Millwall goalkeeper Roberts, who was sent off for the incident.
After the 3-1 fifth round defeat, Neil said: "I think the ball went in behind, Liam Roberts has come out which he has done in many games he's played. He's misjudged it and caught the lad. He has mistimed it, he got sent off which at that stage made the game doubly difficult for us.
"I don't think it is meant. I don't think there is any intent, why would there be intent? We don't want the lad to be injured. We wish him well and hope he is back on the pitch soon. It was a mistiming, he was sent off, he is disappointed and will hope Mateta is fine, which we all do.
"You are playing Premier League opposition on their own ground so it is a difficult task with 11 men. The nature of the goals probably disappoint me the most."