Jefferies says the midfielder, who was signed from Ayr United just before the January transfer window slammed shut, is still trying to find his feet in the SPL.
But he was delighted with Stevenson's contribution after coming on an as an early substitute in the recent win over Hibs and believes he will prove his real worth for the club next season.
"Ryan was played in the team far too early," admitted the Hearts boss. "He just joined us and found himself thrown in the team against Celtic.
"In an ideal world I'd like to have had him on the bench and fed him in after having him training with us a bit longer.
"He's come up from the First Division and still to adjust to SPL. Pressure increases as a result of that because people start asking is he up to the task or not but that's unfair on him.
"However, I think he showed how good he is after coming on very early against Hibs. I thought that was his best for us and that will give him a huge lift and boost his confidence."
Jefferies, who always uses Thomas Flogel as an example of a player needing time to settle in at a new club – the Austrian had a nightmare in his first game against Rangers but became a key member of the Scottish Cup-winning side in 1998 – added: "Ryan used ball sharper in that game and was up on the ball and worked really well.
"There was a bit more sharpness both in thought and in terms of his touch. He is a good passer of the ball but sometimes not got the time he thinks he has due to the fact he's been used to playing in the First Division.
"That will all improve and he'll be one we'll be looking to do well next season. It's a about finding his feet in the SPL this season, getting a good pre-season under his belt and then I'm sure he'll surprise a few people."
As his team headed for Paisley today and a crunch clash with St Mirren, Jefferies admitted the final seven games of the season will determine whether certain players have futures at the club.
"I have an idea of what squad I want for next season," he revealed. "There are players I am not sure about yet so it's up to them to prove to me what they are capable of over the coming weeks.
"If we don't get into the top six that will be looked upon as a failure and we'll have to assess why it happened and make sure it doesn't happen the following season.
"I will give recommendations about what we should do and we will work together to see how we can strengthen the squad and, if we do that, then we've got to make sure we are not scratching about like we are at the moment trying to get into the top six.
"Finishing in the top six will make it a bit easier for us to get into next season and hit the ground running."