Martin O’Neill says last season was a “wake-up call” for double winners Celtic – but are the club acting quickly enough this summer?

In his first interview since being appointed permanent manager on a one-year contract, the 74-year-old has admitted he is expecting “a tough old time” for the Scottish champions in the new campaign.

After Celtic capped a title race for the ages with a dramatic final-day win over long-time leaders Hearts to retain the trophy, O’Neill is braced for another torrid battle with the Tynecastle side and Rangers.

“I think Rangers will get stronger, and Hearts won’t go down without a fight, there’s no question about that,” O’Neill told Celtic TV.

“I felt every single time that we played matches [last season] the teams were getting closer to Celtic than perhaps ever before, certainly in recent times, so those are concerns.”

However, the speed at which the Parkhead club are moving would not indicate a sense of urgency.

After leading Celtic to a league and Scottish Cup double in his second interim spell, O’Neill’s appointment came on 11 June, almost three weeks after the conclusion of the season.

It took a further two weeks before his backroom staff were confirmed, the same day the players reported back for pre-season training. That staff is a coach light after Gavin Strachan left to join West Brom.

“I thought that was very important,” O’Neill said of having Fotheringham and Maloney signed for the upcoming campaign.

“We gel together as much as anything else and I suppose, because the end result was that we won, then you start to feel that it was half decent. So it’s nice to have the staff back.”

Celtic’s playing squad is in urgent need of reinforcements and more quality, yet they are currently one of only two Premiership clubs – Motherwell the other – yet to make a single signing.

Including loanees, Celtic’s departures list this summer could reach double figures and uncertainty surrounds the future of key players Daizen Maeda, Arne Engels and Benjamin Nygren.

The lack of incomings so far is stark. In contract, Hearts have already signed seven players in their squad rebuild. And Rangers – now led by Derek McInnes after his switch from Hearts – have landed Tynecastle striker Lawrence Shankland plus fellow Scotland international Ross McCrorie from Bristol City.

As O’Neill throws himself into planning for the new campaign, he has had little time to digest last season’s success.

Celtic secured their 14th Premiership crown in 15 years in remarkable fashion, winning their final seven matches to snatch a title that had at times seemed to be edging out of reach.

“I feel as if, no it hasn’t [sunk in],” O’Neill said.

“If I’d no longer been at the football club, I think I would have more time to digest it and say, oh that was really great, surreal.

“It feels as if you’re just back in again, and so I probably haven’t got the time. Maybe the first league game at Celtic Park, maybe I’ll think about it then, but genuinely, no I don’t think it has really sunk in.”

The gruelling, draining nature of the job and title triumph left O’Neill unsure if he was open to taking the post full-time this summer. But the potential for regrets pushed him back into the dugout.

“It was strange in the sense that if I’d been asked about it a day after we’d done it, I don’t think I would have had the energy,” he said.

“And I suppose deep down really, if I felt okay by maybe late July, August or September time and things had moved on without me, then you think, oh gosh, maybe I would like to have stayed on.

“So I tried to project myself a couple of months further forward.”

The Champions League incentive also played a part. Celtic’s play-off tie is looming large – the first leg takes place on 18 or 19 August – and O’Neill is well versed in the competition’s importance to the club.

Celtic, then under Brendan Rodgers, suffered a calamitous qualifying exit to Kazakhstan’s Kairat Almaty last summer to set the tone for their turbulent season.

“Absolutely vital,” O’Neill said of reaching the league phase.

“If we’re going to do it, first of all, we’re talking about trying to augment the squad. Secondly, it’s getting players prepared both physically and mentally for those games, and that becomes very, very important.

“The disappointment of last season, not making it into the Champions League because of having a good run the previous year, I think that carried over to league performances. Malaise is far too strong a word but disappointment and concern about everything and as a consequence I think we fell down a little bit but we raised it at the end.

“Now this tie that we will be in, whoever it may be, becomes very important.”

Not only does O’Neill have to revamp the squad – he also plans to adapt the style of play.

In both interim spells last term he admits he was careful not to make too many changes and risk rocking the boat, particularly following the disastrous tenure of Wilfried Nancy.

But after a full pre-season, fans can expect to see some differences in the team’s approach.

O’Neill referenced the powerful, direct and attacking Celtic side of his trophy-laden first Celtic tenure at the start of the century in outlining his vision.

“I think I can marry both in many aspects,” he said. “By that I mean have us play in the manner in which the side maybe 25 years ago [played]. We played very quickly, played with a dash and with a lot of very, very fine players and I think we can marry both.

“When we have possession of the ball it’s great to keep it and absolutely right, but I’d like us to keep it for a purpose.”

And the Northern Irishman is looking forward to having more time to work with the players than when he returned last term.

“I think the players can take to it but the best way to do it and the best way to make these little subtle changes is actually through pre-season,” he added.

“It’s working with the players every single day. We had a rush of games last season including European games, four games in eight or nine days, and you never get a chance to do any of that [subtle change], pre-season will give you that.”