"Celtic can hold onto Brendan Rodgers this summer - by breaking their £6m transfer record on Odsonne Edouard"

Rodgers, who could become the first man to lead a team to back-to-back trebles in Scotland later this month, is one of the favourites to take over from Arsene Wenger at Arsenal at the end of the season.

The former Swansea City and Liverpool manager, under contract with the Ladbrokes Premiership winners until 2021 after signing a four year deal towards the end of last season, has repeatedly stressed he is content in Glasgow.

However, Hartson - who is still, along with his fellow striker and former team mate Chris Sutton, the most expensive player the Scottish champions have ever bought - feels his old club must help him to make progress in Europe to keep him happy.

The Welshman, signed from Coventry City for an outlay of £6 million way back in 2001, reckons retaining the services of Edouard, on loan from French club Paris Saint-Germain until the end of the season, will enable him to do that.

Celtic have first option to sign the gifted 20-year-old – for a fee believed to be in the region of £7 million – and Hartson has no doubts that would be money well spent even though it would be more than Celtic have ever parted with for a player.

"You've now got to back your manager if you want him to continue and take you through the next two or three seasons,” he said. “This is a great opportunity for Celtic to go 'Brendan, we love you here, we want you to stay for the next two or three seasons'.

“Shake off every other offer that comes in for him, Celtic can dismiss that, he's our manager. But you've got to be able to back him in the market as well, show him that you'll support him and you're behind him.

“People like Edouard who, with a little more improvement will take you into the group stages (of the Champions League). You need a better quality. Celtic have lots of quality players, but if you can add one or two every year, who have that little bit of extra quality, that's the key.

“If PSG want a lot of money for Edouard, the board are showing Brendan a real intent to keep one of the super-managers, who's very sought after at the minute.

"If he says 'I really want this player', they might say 'this once, we'll stretch for you'. If the club show that they might get that little bit back from Brendan in terms of staying on."

Hartson was certainly impressed with the display of Edouard, who took his tally for the 2017/18 campaign to 11, with his two goals against Rangers at the weekend and is convinced he will be a good addition to the Celtic squad.

“It was another magnificent decision by Brendan to start him against Rangers at Parkhead,” he said. “There wouldn’t have been a single Celtic fan in the stadium or among the millions watching on television who could have called that.

“The assumption was that Leigh Griffiths would play if Moussa Dembele was injured. Everyone thought that apart from the main man, who works with Odsonne every day and knows and appreciates how good he is.

“He knew he could handle the euphoria and everything surrounding the game, which is very difficult to do. Celtic are riding on the crest of a wave at the minute and Rangers need a lot of help on and off the pitch.

“So starting Edouard was a masterstroke. I think he’s great – he’s quick, powerful and he gets goals. He certainly didn’t let anybody down.”

Hartson continued: “Let’s be realistic about it, Celtic aren’t going to buy anyone for £15 to 20 million because they don’t have that kind of money.

“I think there’s a level they’ll be prepared to go to, but I’d certainly pay £6 million for him. If a deal can be done which suits everyone, I’m sure he’s a player Brendan wants to keep.

“He’s proved his worth so would Celtic stretch to £8 million on the back of the Champions League revenue from the last two seasons? Are they going to sell Moussa Dembele? That would bring in even more funds. But I think, if PSG are being sensible, Celtic would match their price but they won’t pay silly money.”

Celtic have enjoyed great success in the transfer market buying players with potential, developing them over time and then selling them on at a profit and Hartson is confident they could do the same with Edouard regardless of how much he costs.

“Look at the players who’ve been brought to the club and done well and been sold at a big profit – like Virgil van Dijk, Fraser Forster, Ki Sung Yeung, Gary Hooper and the rest,” he said. “That can happen with Edouard.

“If he does very well – if he goes and bangs in 40 goals next season – then his value would suddenly treble so Celtic would certainly look at that aspect. Bargains are sometimes dearer than £2 million and Celtic are in a better position to spend now than they were under Ronny Deila, when they missed out on the Champions League for two seasons and crowds were down to 25,000.

“How much money did Celtic lose out on then? But Brendan has brought the crowds back. There are full houses every two weeks and they’ve also had the three-game Champions League packages and European football after Christmas.”

Rodgers has led Celtic into the Champions League group stages two years running and also through to the knockout round of the Europa League this season and Hartson knows he will want to do even better in continental competition in future.

“That's where Brendan wants to go,” he said. “He's on the cusp of winning a double treble, he'll be setting new targets and setting the team new targets. He'll want them to win the treble again and do better in Europe, that's common sense.

"Every Celtic fan goes to bed at night saying: 'I hope Brendan stays'. I think they'd all be hoping he stays. There's only one who knows and that's him.”