Jelavic struck twice in victory over St Johnstone.
He has 10 goals for the season so far and Smith is confident he will see a return on the £4million Rangers paid for his services last summer now that his injury problems are in the past.
He said: "It was obviously a problem for him and for us as well that we lost him.
"I felt we were signing someone who could get us a lot of goals and I think he has shown that he can do that.
"But the three months that he was out have been a major disruption to his season.
"It's always difficult for a player to come back in and gain the required sharpness.
"He's getting there and will probably be reaching his peak as the season is coming to a close.
"For ourselves, we are just happy that he is back in and scoring goals.
"He could have had a hat-trick in the last couple of home matches and we just need to hope he keeps that going."