Oxford United boss Michael Appleton was left frustrated after their FA Cup defeat to Middlesbrough.

Cristhian Stuani's 86th-minute winner at the Riverside Stadium ended the visitors' hopes of a replay after they had fought their way back from 2-0 down to leave their Premier League opponents in real danger.

Appleton was left to reflect on what might have been, and a winning goal which he felt should have been disallowed for a foul on defender Curtis Nelson by Alvaro Negredo.

Appleton said: "There were no issues with the penalty, it was a definite penalty. I thought Stewart Downing was excellent in terms of he was very clever where he took his first touch and he used the pace of Mags trying to get back in, so I have got no issue with that at all.

"But I have a lot of issues with the one we didn't get and then the one they won with, but I'll leave the officials to describe why that was given and wasn't given.

"Negredo was just pinning Curtis Nelson, he was just grabbing his shirt so he couldn't attack the ball and obviously that affected the first contact.

"They got a little bit of luck - Negredo just got a bit of a nick on it when he tried to do the overhead kick - and to be fair, it was a good finish at the far post."