“I made a note watching Kell Brook on Saturday which said ‘who is fading faster, Brook or Amir Khan?'”

A domestic showdown between Khan and Brook – hyped for years – featured high on the list of bouts BBC Sport boxing correspondent Mike Costello had looked forward to in 2018.

But how much does either man have left? And will a fight between the two former world champions sell out a stadium?Costello and BBC Radio 5 live analyst Steve Bunce have had their say.Listen: Now or never for Khan v Brook?

Hard years taking a toll on Brook?

Khan blitzed to a first-round win over Phil Lo Greco in April and survived being knocked down to beat Colombia’s Samuel Vargas in September. Brook also has two wins this year, returning from surgery on both eye sockets to stop Sergey Rabchenko in March, before battling to an unimpressive points win over Australia’s Michael Zerafa on Saturday.

Bunce: There were times where Brook looked old, slow, predictable and confused against Zerafa. But, at the same time, he probably lacked motivation.

He fought Gennady Golovkin, which was sold out, and he took a beating. Then we had him in front of 40,000 against Errol Spence Jr, taking a similar beating. Zerafa is not Golovkin or Spence and perhaps Kell had that in the back of his mind.

Kell was a kid I wrote about when he was about 10 years of age. He is 32 now and has had a life in boxing, and some of it has been hard. He is not a silver spoon fighter. He had two horrible fights. He’s not had a straightforward life and it catches up with a kid.

Before his fight I’d have said Khan had lost more of what he had, but still had plenty left. After the bout I am wondering who is fading faster? It is a perfectly valid question and I’m not sure.

Costello: Brook went into the fight as a 1-50 favourite with some bookmakers but he didn’t perform like one. But I always say you need at least two rough displays before you can make a judgement because of things like motivation. He was aware of the type of odds and opponent he was facing.

One of the hallmarks of Brook down the years has been his reactions and reflexes – they weren’t there. Time and again he was leaving his his left jab hanging and was open to the right hand.

I made a note watching him which said ‘who is fading faster, Brook or Khan?’

Hope of a battle between fading forces

Khan is said to be in talks with WBO world welterweight champion Terence Crawford but promoter Eddie Hearn says he will earn double the money for facing his British rival and expects to know if the pair can finally agree a fight in the next 10 days. In order to make the bout, Brook has publicly said he would drop to the 147lbs welterweight limit, a mark Bunce feels he has struggled to make “for 10 years”.

Bunce: Eddie Hearn has not put a foot wrong for several years – everything he has touched has come out well and we have all benefitted.

There were the first signs of discontent when he failed to secure Deontay Wilder v Anthony Joshua. If he can’t get Wilder v Joshua, can’t do Khan-Brook and has now lost Tony Bellew to retirement, this is a fight Hearn maybe needs to deliver next year.

But maybe Khan is looking at a bigger plan – he loses to Crawford and still has a fight with Brook. I don’t think you can blame Khan, he’s just considering other options. If something crazy and sexy popped up for Brook, he would do the same.

Other than that, Brook can’t go down to welterweight and mix it with Crawford or Spence as he’s already done that and it didn’t work. If he stays at light-middleweight, whatever you create, you don’t get anywhere near the hype of a Khan-Brook fight.

I think it’s moved from a stadium fight to a really big indoor fight. There was a period a few years ago where it was a 60,000 stadium fight but that was a fleeting moment before Brook lost to Golovkin and Spence, and Khan was laid out cold by Saul ‘Canelo’ Alvarez.

It will still sell and do unbelievable business.

Costello: It’s a difficult future looking ahead for Brook. The champions at welterweight or light-middleweight, they are all very good performers. So for Brook, they would be a huge risk against not massive financial reward.

A Khan fight provides this monster pay-day in a fight which would go a long way to creating a legacy for either man.

It isn’t the contest I thought it would be when we moved into 2018. It was very high on my list of domestic clashes but is nothing like as attractive. The sliver of hope I cling on to is that one of the greatest fights of all time – the ‘Thrilla in Manila’ where Muhammad Ali met Joe Frazier in 1975 – was between two men who were way past their best.

Best guess for me is money talks, Khan v Brook will happen.