They are uncompromising rivals in a Premiership campaign when the stakes have rarely been higher on the Old Firm battleground.
But Ryan Jack has no doubts he and Callum McGregor can also be highly effective brothers in arms when it comes to Scotland’s quest for a place in next summer’s European Championship finals.
By the time that tournament comes around, either McGregor will be celebrating a domestic season when Celtic have clinched an historic 10th consecutive league title or Jack will be savouring having helped Rangers dethrone their greatest foes.
For Scotland manager Steve Clarke, however, it is a burgeoning midfield partnership between the pair which offers huge encouragement ahead of the national team’s return to action against Israel on Friday night after a 10-month hiatus.
McGregor and Jack combined impressively when they were deployed at the heart of Clarke’s side last November, their solidity and tactical awareness a key factor in the victories over Cyprus and Kazakhstan.
“The last couple of Scotland games, I really enjoyed it,” reflected Jack. “It was two strong team performances, I wouldn’t just say it was down to two individuals in Callum and me.
“But we got on really well during the game and as a team I thought we did well. Whoever the manager goes with, I am sure we will be looking to have two strong performances again against Israel and the Czech Republic during this international break.
“When you are playing at club level, it doesn’t matter who you are playing against, whether it is Celtic players, Aberdeen players or whoever it may be, it is always going to be fierce and there are always going to be battles. We are rivals.
”But when you come away with Scotland, it changes and you are all striving and pushing for the same objective for the nation and the country. When we come away, club level gets put to one side and that is the way it should be. When you play games, we are all striving to do well for Scotland.”
At 28, Jack is a late bloomer at international level as he prepares to earn just his fifth senior cap this week. But his excellent form for Rangers, where he has become an influential figure under Steven Gerrard’s management, has strengthened his claim for a regular place in the Scotland starting eleven.
“It’s a hard battle in the midfield area,” he added. “There is a lot of talent in the Scotland squad when you look at the midfielders and there are so many playing at a top level, both domestically and in Europe.
“But it’s good because you come away and test yourself, and look to put in a shift to get in the manager’s thoughts and plans. This trip is no different. We all want to play but if you do well in training, then hopefully that’ll be enough.
“The plan is to take my club form into Scotland duty. Everything is going well at Rangers and it’s always an honour to get picked by Scotland.
“Personally, I am in a good place physically and mentally. I had a good pre-season and that always stands you in good stead going forward.
“I have played a lot of football since we started back. Hopefully I get the chance to play in these games but there is a lot of hard work ahead.
“When the gaffer (Gerrard) first came to Rangers, I knew I would have to work hard. I’d just come off a bad injury and I hadn’t really played much football. It was going to be tough to work myself back and get into his plans.
“At the time, I would have thought that being in the position I am now would have been a fair bit away. But I just got my head down and worked hard at Rangers.
“Steve Clarke (pictured left) then came in as Scotland gaffer and really believed in me. He called me up, I get on great with him and now I am looking forward to being part of these games.”
Jack could be joined in the Scotland side by his club-mate Jon McLaughlin, the former Hearts and Sunderland goalkeeper currently keeping Allan McGregor out of the Rangers side since his summer move to Ibrox.
McLaughlin, pictured, has been part of a Rangers defence which has started the league season with a Scottish record-equalling six consecutive clean sheets, while recent Scotland number one David Marshall has not played a competitive fixture since March.
“I don’t know if it really affects goalkeepers too much in terms of how much football they play,” said Jack. “The only thing I can say is that I have played with both internationally and now Jon at club level and they are both top, top goalkeepers. I am sure they will both be fighting to get the number one spot.
“Jon has been excellent for Rangers so far. Allan McGregor had a knock and that is how Jon has got his chance. I had been in Scotland squads before with Jon so I knew what he was capable of and I am sure he will be pushing and trying to be number one.
“But David has been a very strong goalkeeper over the years and I am sure he will want to be number one as well. It is tough competition all over the pitch and that is the way it should be at international level.”
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