The subject arose last week when Carlos Cuellar left Rangers for Aston Villa after triggering a clause in his contract which said he could leave Ibrox if the Govan club received a bid of 10million euros (£7.8million) for his services.

Celtic today completed their fourth summer signing when Cardiff defender Glenn Loovens penned a four-year contract.

He joins fellow recruits Marc Crosas, Paddy McCourt and Georgios Samaras in the first-team squad.

Meanwhile, Artur Boruc, Scott McDonald, Shunsuke Nakamura and Aiden McGeady have been handed contract extensions in recent months, keeping Lawwell busy in negotiations.

The Celtic chief executive admits the exit clause is part and parcel of modern-day transfer negotiations but he told PA Sport that it is not a concern of anyone at Parkhead at the moment.

He said: "The exit clause is a normal part of transfer negotiations these days, it's not unusual.

"During my time here we have been asked to include exit clauses in contracts but have managed to resist it.

"Sometimes players ask for an exit clause and less money but we don't have any players at the club who have one."

While Celtic look to capture their fourth Clydesdale Bank Premier League title in succession, the Parkhead club revealed an encouraging set of financial results.

The results, which are for the year ended 30 June 2008, show profit before taxation is £4.44million, down from £15.04million from last year with bank debt down from £4.99million to £3.52million net of cash. Lawwell insists the club has never been in better shape but admits the cash generated from the Champions League goes a long way to keeping the club's finances in rude health.

"Champions League football is crucial to keeping a Champions League squad," he said. "It's vital that we play in Europe.

"It is good in the short term for finance and good in the long term for profile. "We are now seen as a big club.

"That's why we can go to Japan and attract players like Shunsuke Nakamura."

Celtic return to Tannadice tomorrow to face a Dundee United side who suffered an opening-day defeat against SPL new boys Hamilton Academical last Monday.

Manager Gordon Strachan insists he was not surprised about Accies' win but is expecting United to show their true form tomorrow.

He said: "I watched the game and it was a game between two good sides and Accies did very well.

"A lot of teams who were in the bottom six last year put in good performances in their first game so it didn't surprise me that Accies did the same.

"We will look at what we've got first but United are a good side.

"They have got good players who have did very well last season.

"Noel Hunt has moved on and he was a good player for them but they keep turning up good players.

"They do their homework well and work very hard to get players in so you've got to compliment them on that."