While Dark Blues head coach Scott Johnson has named the Saracens forward skipper every time he has played, the Australian has steadfastly refused to make the appointment permanent - until now.
But the Australian has warned the 31-year-old former Glasgow man that his place in the side is not guaranteed ahead of the RBS 6 Nations - and confirmed he will only play at openside flanker after admitting he has better options on the blindside and at number 8.
Johnson, who made his comments as he announced the 36-man squad he will chose from ahead of the tournament, said: "I've told Kelly to his face - and there's no use running away from it - if he is good enough to get in the starting XV, he will lead the team.
"But we are only viewing Kelly as purely a number seven now. The six and the eight roles we will leave to other people but he has to cement his place at number seven.
"If he is good enough to do so, he will captain the team. If he's not, we will look for someone else."
Johnson preferred the likes of David Denton and Johnnie Beattie in the six and eight roles during the autumn internationals but insisted there is still room for Brown in his back row.
"We have some good six and eight athletes coming through," said the head coach.
"We need to compete athletically against the bigger nations and we have guys coming through who we feel can do that. Therefore I want to encourage the growth of those players.
"Kelly fits a different mould. He's done really well for Saracens at seven over the last five or six weeks so moving down the path that will be his spot."
Johnson has named uncapped duo Dougie Fife and Chris Fusaro among a group that will meet up in Edinburgh next week for a pre-tournament get-together ahead of their Six Nations opener against Ireland in Dublin on February 2.
Edinburgh winger Fife is called up for the first time, while Glasgow flanker Fusaro will hope to make his first appearance for the Dark Blues after failing to see action during last year's tournament.
Johnson handed out a raft of caps to untested players during 2013 as he sought to leave an experienced squad for Clermont Auvergne coach Vern Cotter, who takes over from the current boss next summer.
And he believes the latest two newcomers are worthy of their place.
"We have capped a few over the last 12 months, it's fair to say," he said. "But we have now got a couple more in there for this squad because they deserve the right to be there.
"Chris has been picked on form and it's nice to have him back. He is an interesting one. We gave him a clear directive at the start of the last campaign when he was a sub.
"We told him what he needed to improve on and we've been happy with how he has done since. I thought he was outstanding last weekend. He has shown some great resolve and his inclusion is just reward.
"As for Dougie, we are looking forward to seeing more of him. He gives us a bit of growth in a position where we are not overly strong."
Missing from the group are injured Glasgow duo Alastair Kellock and Peter Horne, while Edinburgh's Tim Visser and Euan Murray of Worcester also miss out.
Glasgow scrum-half Henry Pyrgos, meanwhile, drops out of the squad altogether after Johnson named only two number nines, Edinburgh's Greig Laidlaw and Pyrgos' Scotstoun team-mate Chris Cusiter.