Two-division world champion Shawn Porter believes the junior middleweight fight between Jermell Charlo and Tim Tszyu is now becoming a very tight encounter.

Charlo, the undisputed world champion at 154-pounds, has been inactive since May of last year, when he picked up a knockout win in his rematch with Brian Castano,

Tszyu is Charlo's mandatory challenger under the WBO.

After several delays to their fight - due to Charlo suffering a severe hand injury in training camp - Tszyu has chosen to stay busy.

Back in March, Tszyu picked up a knockout win over former WBC world champion Tony Harrison - the only fighter to hold a win over Charlo.

On Saturday night (Sunday in Australia), Tszyu will return to the ring once again, when he faces tough Mexican contender Carlo Ocampo.

The WBO has ordered Charlo to face Tszyu by the end of September.

And when they finally meet in the ring, Porter expects a much closer fight than it would have been when the contest was first ordered last year.

“A year ago I would have said Charlo wins that fight, easy. After seeing that fight against Tony … Now? With Tim busy, keeping that workrate up and riding the waves of energy of being consistently successful, this fight is going to be harder for Charlo," Porter told The Sydney Morning Herald.

“If [Tszyu] does something amazing, something no one has been able to do and knock out Ocampo - Errol [Spence Junior] stopped him, but it was a body shot - if he beats down Ocampo and knocks him out, that’s something for me to write home about.

“The more time Charlo stays out of the ring, not fighting, and especially with Tim getting into the ring and fighting, it’s just becoming a harder fight for Charlo. It may even be 50-50 now. I see Tim really maturing. When you get in the ring with someone and they say, ‘Who have you fought?’, each fight is a step up the ladder.

“I believe that Tim is taking all the steps and Charlo is staying here. It’s only a matter of time before he goes here [on the same level]. And on fight night, he could do that [go another level]. That remains to be seen, but right now I think it’s a 50-50 fight.”