Stevenson came back earlier than anticipated from a torn hamstring to help Hearts, who are 13 points adrift of safety, end a five-game losing streak with a 1-1 draw against St Mirren on Sunday.
Jamie Hamill, who with Stevenson is the only other outfield player aged over 27 in Locke's squad, struck a spectacular equaliser and the Hearts boss knows the pair will be crucial when his administration-hit side bid to get into a positive Scottish Premiership points tally when they play Hibernian on Thursday.
Locke, who is still missing Jason Holt, Gary Oliver and Mark Ridgers through injury, said: "I've got a lot of confidence in the players here. I've said all along they are a young squad but, at the same time, we aren't in the position this season that we can afford five injuries.
"I'm not one for making excuses, it's not in my nature, but with having five players out, that's a crisis for us.
"I've not got a lot of experienced players but the ones I have, when they are playing well, are a massive influence on the team.
"The last five weeks I have struggled to put players on the bench.
"I have said all along we will give ourselves a chance if I can get everybody fit. I've not really had Ryan Stevenson for most of the season.
"If he can keep himself fit, anyone can see he is a huge asset to the team."