Glowering at one another used to be the least of it when Paul Hartley and a young Scott Brown came up against one another on opposite sides of the Edinburgh divide.

On Sunday afternoon, they will seek one another out in the aftermath of a game at Dens Park, a game that still holds the tentative possibility of delivering a title depending on what happens at Pittodrie 24 hours earlier, but where there was once hostility there is now only respect and mutual admiration.

Having swapped Hearts and Hibs respectively to become team-mates at Celtic Park during Gordon Strachan’s era for two years, Hartley got to know Brown not as the guy he loved to hate, but as a player who had much more to his game than just aggression and antagonism.

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Those elements remain, yet this season has underlined that the Celtic skipper has a little more sophistication to him. Brown has been integral to the way that Brendan Rodgers has implemented his own pressing, penetrative style of play and the influence of the 31-year-old has not been lost on Hartley.

“I think he has matured as a footballer,” said the Dundee boss, who lifted the Ladbrokes Manager of the Month award for February at Dens Park yesterday afternoon. “He is having an outstanding season the way that he is performing.

“ He looks injury-free, he looks strong, fit. I think Scott is a real leader for that group. When I played against him I didn’t really like him! He is one of those guys that I didn’t like when I played against him because we had such good battles but then when you are a team-mate, you appreciate him not just on the pitch – he is a real gentleman off the pitch.

“I can still pick the phone up to him and ask for anything. He was annoying. He did everything – he would annoy you, slag you, he would be cheeky, he would kick you but he was an outstanding prospect.

“We had great battles but we are good pals now. He is a guy you want in your team and he has found a new level this season. I think that comes down to the work that the manager has done with him on the training pitch.”

Brown is not the only guy at Celtic that Hartley can still lift the phone to.

The former Hoops midfielder, who part of the side who came back to win what had looked like an improbable title on the last night of the season in 2007-08 with victory over Dundee United at Tannadice, has also established a rapport with Rodgers.

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The Celtic manager offered his number on his inaugural meeting with Hartley and the Dens Park boss believes that the influence of Rodgers has had an uplifting effect on the league as a whole.

There has been criticisms, some more vocal than others, about the way that Celtic have dominated the domestic landscape this season after dropping just four points in the 28 league games they have played.

Celtic remain unbeaten and odds-on for only the fourth Treble in their history. What appears obvious, though, is that Rodgers has raised the profile of the league and while onlookers may not be favourable with their observations, there is a feeling that the Celtic manager has contributed to elevating the standard.

“There has been a lot of negativity surrounding the game, not just domestically but around the national team too,” said Hartley. “Bringing him in and the quality of football that he has brought to football has been good to watch. You always want to pit your wits against the top managers and there is no doubt that Brendan is one of the top managers in Britain.

“You seen his record at Liverpool and at Swansea and for me to go up against Brendan Rodgers, it has got to be something that you enjoy.

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“He's an outstanding manager and someone who's got a lot of time for other managers when he comes in the office. Somebody that I think you can pick the phone up to and talk to. Any time he's been in and we've been in his company, he's been excellent.

“We've had a chat and a couple of text messages. The last time he came into the office, he gave me my number straight away.

“That tells you the type of person that he is. He's got time for everybody involved in the game. He's done an outstanding job. He's an excellent manager and you anybody that talks about him, the way that he works and his man management, he has something about him. I think he's been an excellent addition to Scottish football. Something we that we did need.”