The former Falkirk captain missed Saturday’s 2-0 defeat to Aberdeen after the problem recurred at training on Thursday.
Barr has been troubled with the injury since the agonising 17 March League Cup final defeat by St Mirren and was forced to drop out of the squad for the weekend’s match at late notice.
Hearts host Ross County on Saturday in their final pre-split match and return to action on 20 April following a fortnight break. Locke hopes Barr – out of contract this summer – can play a part in their final six matches of the season. He said: “It was a disappointment. He has been struggling with an ankle problem for a couple of weeks.
“It flared up again on Thursday, we tried it on Friday but it was not to be. It’s a bad ankle injury and it’s one of them that if he keeps trying to play through it, it’s only going to get worse. We’re hoping, with a few days rest, it will be OK.”
Hearts have conceded four goals in their last two outings and Locke reckons a distinct change in formation since John McGlynn’s departure as manager could be the reason behind their vulnerability in defence.
He added: “We have tried to be more positive going with the two strikers and you maybe do leave yourself more open at the back. It didn’t help losing Darren, who can sit in front of the back four and mop things up.
“We work on things as a team and I’m not just blaming the back four. We have to defend better as a team.”