The striker's performances in his two outings under new boss Paolo Di Canio have shown a major improvement.
The former Swansea marksman said: "It is unfortunate Steven got injured.
"He has been a vital part of the club this season and scored 11 goals. It was a massive blow to the team.
"However, that gives opportunities to other people and you have to take them. I will hold my hands up, in my first few games, my performances were not too good.
"However, I have set my standard now and hopefully I can maintain that."