"He has actually had two really awkward games to play in, away at Tynecastle and away at Tannadice," said Smith.

"Both are very difficult places to go and play in and you have got to appreciate that factor.

"If we hadn't been a goal down against United, I wouldn't have taken him off. I had to do something more in an attacking sense at the start of the second half to try to mix the game up a bit and that's why I made the substitution."