Alan Pattullo: Aberdeen and harsh truth of Rangers boss Pedro Caixinha

Last month's Scottish Cup final against Celtic looks like being Derek McInnes' last game in charge of Aberdeen. Picture: John Devlin

“Concentrate on your own club,” he told Caixinha. In addition, McInnes called Rangers’ own efforts to finish second an “embarrassment” given their budget. The spiky reaction spoke volumes.

While this was all good, knock-about, tail-of-season newspaper material, the rattle from two temporarily warring managers couldn’t deflect from the accuracy of Caixinha’s statement. A cold, inescapable truth has been creeping up on Aberdeen for some time now.

The club is being undermined by departures, some confirmed, others speculated, as critical members of playing and coaching staff wonder whether the Pittodrie club have gone as far as they can at the present time. Niall McGinn has already left, while Jonny Hayes is a target for Celtic. Now McInnes is set to depart for Sunderland, taking assistant Tony Docherty with him.

No new stadium, perhaps no wingers and now possibly no manager. What was that about the end of a cycle?

Yesterday’s news that McInnes is now in talks with Sunderland means the red warning light is flashing even more brightly for Aberdeen. Caixinha was broadly correct with his assessment.

While Aberdeen and Sunderland are still negotiating, it might be premature to proclaim the end of the McInnes era. But there’s every reason to believe he will find this opportunity difficult to resist. With a jump straight into a Premier League job unlikely from Aberdeen, the Stadium of Light post is perhaps the next best thing. Sunderland are a Premier League club in all but name. They have the riches to further enhance this claim due to the windfall payment guaranteed to clubs relegated from the top flight.

Following a delay in Aberdeen’s new stadium plans it’s a sensible time for McInnes to consider a return English football. Fiercely ambitious, he will relish the chance to lead a team into the Premier League, as he did as skipper of West Bromwich Albion in 2002. His stock is as high now as it’s potentially ever going to get in Scotland. While there are plenty of pull factors, financial chief among them, there are push factors also. McInnes, conscious of Rangers’ extensive re-strengthening efforts, will wonder if he has achieved all he can at Aberdeen. Jimmy Calderwood, one of his Pittodrie predecessors, often spoke of the four-year shelf life of managers.

McInnes’ reign began in March 2013, just over four years ago and following Craig Brown’s success in halting the club’s most recent slide. Since then McInnes has helped Aberdeen gradually improve to the point where they have become the second-best team in Scotland. But as Caixinha somewhat impishly suggested, this status is pending.

This does feel like the end of something. And what do Aberdeen have to show for Rangers’ denuded, post-2012 state? Not enough perhaps – only a League Cup victory over Inverness Caledonian Thistle on penalties, following a 0-0 draw.

Even McInnes acknowledged this doesn’t quite merit a place in any Scottish football Hall of Fame. However, this was before the extent of Celtic’s recent invincibility became clear.

Speaking prior to the first of two cup final appearances against the Parkhead side last season, McInnes noted how “any team can win a trophy”. He added: “For me a period or an era is synonymous with winning trophies and we’ll only really look back at this period if we can win more than one trophy.”

In this same press briefing, McInnes rightly praised his side for showing “real consistency” in the league. Had Celtic accepted another season of Ronny Deila’s stuttering stewardship, then Aberdeen might have challenged for the title last season.

Deila provided Celtic with plenty of notice of his intention to depart, meaning Celtic had Brendan Rodgers lined up and ready to go on 20 May last year. It’s now nearing the middle of June. The danger is Aberdeen have been caught with their head in the sand, unprepared, or unwilling, to contemplate a post-McInnes landscape after growing so comfortable under his strong leadership.

If their manager does move to Wearside, there will be an attendant fear for Aberdeen about losing other pivotal players, including goalkeeper Joe Lewis – Sunderland have just agreed a £30m deal to sell their highly-rated No 1 Jordan Pickford to Everton – and Shay Logan, the Pittodrie club’s excellent right-back. Both could become targets for McInnes, for whom funds will not now be an issue.

It isn’t the first time Aberdeen have had to replace a successful manager, of course. They know the potential for disruption and how the impact can last years.