The former Falkirk player missed last week's defeat 2-0 to Aberdeen with what the Gorgie boss described as an "ongoing" problem.
And with a free weekend following the visit of the Staggies - when the William Hill Scottish Cup semi-finals take place - Locke is of a mind to allow Barr more time to shake off the injury.
"The squad is pretty much the same as last week," he said. "All our injuries are long-term so it's not as if we've got the satisfaction of getting one or two back.
"All the boys are out until the end of the season and it looks like Darren Barr will be struggling with an ongoing ankle problem.
"Looking at it sensibly, we've got no game next weekend so if he misses this match then he's given himself three weeks to get it right and that's the right thing to do with five important games after the split."
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- Darren Barr