Celtic manager Martin O'Neill has made it clear he wants to keep his key players despite growing transfer interest.
The club is preparing to start its Scottish Premiership title defense against Dundee on Monday.
The Scottish champions have seen 14 players leave this summer, including winger Daizen Maeda to Ipswich for £10 million.
Joel Mvuka and Junior Adamu have also departed.
Premier League clubs are circling, with West Ham submitting an opening bid for midfielder Arne Engels.
Everton manager David Moyes has also made contact regarding Canadian right-back Alistair Johnston.
O'Neill confirmed that West Ham's offer for Engels did not meet Celtic's valuation. He also addressed the ongoing interest in Johnston, who impressed at the World Cup.
"Everton have been in contact," O'Neill said. "I'm not sure whether there has been a bid in for that one.
In fairness, David [Moyes] did call me last weekend to tell me that there would be contact.
But I don't know how far that has progressed, or if it has at all."
Concern Over Squad Turnover
During his pre-match press conference, O'Neill expressed concern about the number of exits compared to incoming players.
"I was hoping as each day went past that there wouldn't be any serious interest. But that was never going to happen.
Now that you say 14 [players who have left] I'm worried myself," O'Neill said.
Celtic's recruitment team has spent around £17 million on two central forwards. Kasper Hogh arrived for a club-record £11 million, while Camilo Duran joined for £6 million.
O'Neill indicated he is willing to adapt the team's traditional 4-3-3 system to accommodate both new signings.
"I would think that given the time that the two players should be able to play together without a problem," O'Neill said.
"I don't know what that means, changing systems, changing all that type of stuff. But, they're good players."
Duran has scored three goals in three preseason friendlies and has shown versatility by playing out wide.
"He [Duran] has played out wide as well, so that's encouraging. I'm not so sure that's eventually where I'll play him.
I see him being able to play as a striker or just off the striker," O'Neill said.
Reflecting on his previous tenure at Parkhead, O'Neill noted how squad structure dictates formation adjustments.
"We played a sort of a 3-5-2 for a lot of times," O'Neill said.
"But then we changed it when some teams cottoned on to it, in European matches as well. And then we ended up changing to 4-4-2.
We played that very often. But we had serious running power wide, which was great in those days."
O'Neill stressed that modern teams must be dynamic during matches.
"If it meant us having to adjust to get them [Duran and Hogh] to play together, that shouldn't be a problem.
Famous last words, but it shouldn't be," O'Neill said. "And this is the point.
We should be able to adapt. We've played this 4-3-3 system for quite some considerable time.
It's been successful, which is fine, but we should be able to adapt during the course of the game.
It's only a matter of changing people 10 yards in, 10 yards out. There's not much more to it than that."
Celtic is also in talks with Paderborn for midfielder Mika Baur and Frosinone winger Fares Ghedjemis, who scored 15 goals last season.
O'Neill explained the financial gap between Scottish football and top European leagues when pursuing transfer targets.
"I've got plenty of confidence that we can get the players in," O'Neill said. "Obviously, we're hoping that.
It's not easy. If some good players go, you're trying to replace them.
We're a selling club because of the finance. The finance here in Scotland is just not there.
And I think, way back 25 years ago, when I was able to sign the likes of Sutton and Hartson, I think the gap between that and an English Premier League wasn't as great.
I could be able to get those players up. Actually, they wanted to come.
But it is difficult.
And the difficulty is letting some of your best players go and trying to replace them with, obviously, less revenue and trying to make them as good or, eventually, better than what you let go.
That, eventually, has its problems."
The manager confirmed he has held direct talks with prospective signings during a recent trip to London.
"Yes, we actually have spoken to other targets," O'Neill said.
"There is a definite strong willingness for players to want to come to the football club, which is very encouraging.
Some other ones who might be using you to try and force a move into the Premier League or something, fine.
You can see through that quite quickly.
But at the end of it all, yes, I'm hopeful because I think there's a strong willingness for deals to be done.
We're working with things.
Some things we thought that we were well down the line with have been thwarted by things that were actually outside our control, believe it or not.
I won't go into detail. There's a couple of things that are progressing pretty well as we speak.
So, I'm hopeful. If you said to me, at 14 out and we've got half that number in...
if half that number are going to have a real impact on the football club over the season, I would be satisfied with that."
O'Neill also faces the challenge of preparing for upcoming Champions League qualifiers while managing potential exits.
"In an ideal world, I would love to do that," O'Neill said. "I don't know what might happen.
At this minute, that's the thing that was in front of me for the West Ham thing. So, we're a long way away from that.
But things can happen very, very quickly. That would be something.
One part of me is trying to cater for players possibly leaving.
It is pressing because we'd like to have as strong a squad as possible for those Champions League games."
O'Neill praised the club's recruitment staff for their diligence in identifying options.
"In fairness to the recruitment side, they are very diligent," O'Neill said. "Seriously, they are.
There's options.
Some that might be well and truly beyond us, might be silly, there might be more interest in trying to keep a player here rather than develop the option.
But overall the recruitment staff hand me information all."
Ahead of the Dundee match, midfielder Benjamin Nygren is back to full availability.
Defender Auston Trusty has returned to training after personal leave in the United States, while Liam Scales remains suspended.
