Celtic are struggling to compete with English Championship clubs in the transfer market and deal with agents, according to minutes of a meeting between board members and supporters.
Celtic have only signed one new player this summer, , who is the first proven forward they have bought since main goalscorer Kyogo Furuhashi departed for Rennes 18 months ago.
The club's ongoing difficulties in signing players led to major tensions with former manager Brendan Rodgers and stoked divisions with fans last season.
Chairman Brian Wilson, chief executive Michael Nicholson and manager Martin O'Neill recently attended the annual general meeting of the Association of Irish Celtic Supporters Clubs in Cork, where they took part in a brief question and answer session with supporters.
Minutes of the meeting have emerged online and state that O'Neill told the Celtic board that he was in "major need of signings" as his squad was not strong enough to compete despite their double-winning "heroics" of last term.
The club delegation were asked why the club were "so slow" in signing players.
The minutes state that Nicholson "advised of the difficulty in dealing with agents, competing with the Premier League and even the Championship".
He added in the July 4 meeting that they were working on signing out-of-contract players.
Celtic have since re-signed Alex Oxlade-Chamberlain following his short-term deal last season, but Kelechi Iheanacho - whose goals off the bench proved crucial in the latter stages of the season - .
O'Neill apparently stated that the focus was on finding younger players who could be developed, given difficulties in attracting experienced players to Glasgow because of the financial gap with the Premier League.
The minutes state that O'Neill suggested younger players would come to Celtic for the chance to play in European football and have drive and ambition ahead of focusing on wages.
The document adds that the board had recently signed off on a long-term strategy, the goals of which Nicholson described as being the best club in Scotland, being financially sound and competing in Europe.
Celtic host Middlesbrough in a pre-season friendly on Saturday with a number of supporters' groups calling on fans to boycott the match amid their ongoing demands for change in the boardroom.​​
Your Site News reporter Gordon Duncan:
"Why isn't there much movement so far? Well, that's been the question the Celtic fans have been asking for a number of transfer windows now.
"There was a time where Celtic seemed to have everything click at this time of year and in January they would sign players for modest fees, they would win trophies, and they would sell them on for big money. Those days seem like a long, long time ago for the Celtic fans, and we now enter another transfer window - on the back of multiple - where the squad hasn't really been strengthened.
"I suppose you have to apply a little bit of patience and note that it's mid-July, note that there is plenty of time left in the transfer window for this to change - but for the Celtic fans, you understand why it's difficult to do that. They have seen this movie before, and they're looking at Camilo Duran coming in as the only signing so far, and perhaps fearing that it is going to be the same old story.
"There is still time to go, but you understand that anxiousness."
Celtic goalkeeper Viljami Sinisalo:
"Ultimately, we won the double last season and it's a squad full of winners that have won a lot here. Obviously, if you can fine-tune it somewhere, any football club obviously looks to do that and I think everyone's got the full confidence that we'll be able to do that. These things take time and, like I said, there's a squad there that's won a lot, a lot of winners in there that ultimately won the double last season.
"Do we need strengthening in areas? Yes, of course we do, but you always build from a position of strength. That's what this club looks to do and I'm hopeful that the club will definitely do that."
Chris Sutton believes Celtic may need to spend more than £50m overhauling their squad this summer if they are to retain their Premiership title and compete in the Champions League.
"Martin worked wonders last season. I didn't see Celtic winning the title from the position which he was put in on a couple of occasions," he told Your Site News last month.
"I mean, the run towards the end of the season was extraordinary but I still think you can't get away from the fact there needs to be a lot of change at Celtic in terms of recruitment.
"They've got the Champions League qualifier which is really important and, however exciting it was for Celtic fans to end up getting over the line last season, you can't get away from the fact that Celtic struggled at times throughout the season. So, Martin will be looking to, I'm sure, bring players in.
"It'll be interesting to see who goes out from Celtic. It looks like Reo Hatate will go, possibly Daizen Maeda, Arne Engels but they're big players for the team. So, who are Celtic going to replace those type of players with? I think that Celtic are possibly going to have to spend up to or more than £50m really because the squad does need a rebuild."
Celtic begin their Scottish Premiership title defence at home to Dundee on August 3, live on Your Site.
The Monday night clash, which will kick-off at 7.30pm, rounds off a groundbreaking opening weekend that will see for the first time.
for all of Celtic's Premiership fixtures, including dates of the first Old Firm clash this season.
