Petr Yan has taken a dig at Conor McGregor's cardio after 'The Notorious' invited him to Ireland for a special sparring session at the Crumlin boxing club. 'No Mercy' ridiculed the former two-division UFC champion by asking if he was up for a 12-round outing.Yan and McGregor have been having a go at each other since yesterday on social media. Both have stressed that they are the "best striker" in the UFC. The Russian even challenged the Irishman to a contest at any weight class.Many MMA pundits and fans have spoken about McGregor's apparent fading stamina. Yan has now joined the brigade, escalating the pair's Twitter battle."Maga, we can play if you don’t want to decide matter seriously. Just let me know if you will have enough gas for 12 rounds, kid. Sláinte."Petr “No Mercy” Yan@PetrYanUFCMaga, we can play if you don’t want to decide matter seriously. Just let me know if you will have enough gas for 12 rounds, kid. Sláinte twitter.com/thenotoriousmm…Conor McGregor@TheNotoriousMMA@PetrYanUFC Lol, no prob littler. We will set up a spar or something similar in the near future. Will host you and your team in Ireland for one of our shows at Crumlin boxing club. We will figure it out then, kid. God bless ya. @ParimatchGlobal, get this set.8:54 AM · Nov 12, 20211718116@PetrYanUFC Lol, no prob littler. We will set up a spar or something similar in the near future. Will host you and your team in Ireland for one of our shows at Crumlin boxing club. We will figure it out then, kid. God bless ya. @ParimatchGlobal, get this set.Maga, we can play if you don’t want to decide matter seriously. Just let me know if you will have enough gas for 12 rounds, kid. Sláinte twitter.com/thenotoriousmm…McGregor is currently out of action due to a broken leg he suffered during the UFC 264 main event against Dustin Poirier. He's hoping to return to the octagon in 2022.Petr Yan will likely take on Aljamain Sterling in a bantamweight unification bout next yearInterim bantamweight champion Petr Yan will almost certainly square off against 135-pound titleholder Aljamain Sterling in a unification encounter sometime in 2022.Earlier this year, Sterling became the first champ in UFC history to win a title via disqualification. Yan dropped the belt after delivering an illegal knee at UFC 259 in March.MMA Junkie@MMAjunkieAljamain Sterling says Petr Yan earned an "ass whooping" with his interim title win at #UFC267.Full Twitter reactions: bit.ly/3pT6g0e2:28 AM · Oct 31, 202151814Aljamain Sterling says Petr Yan earned an "ass whooping" with his interim title win at #UFC267.Full Twitter reactions: bit.ly/3pT6g0e https://t.co/tm5zdQRx5Q'No Mercy' defeated Cory Sandhagen at UFC 267 in Abu Dhabi to win the interim championship. 'Funk Master' was initially scheduled to make his first title defense on Fight Island. However, a neck issue ruled him out of the bout.Yan and the No.3-ranked Sandhagen put on a war on October 30 and fought to a unanimous decision, which went in the former's favor.Several people in the MMA world have called Petr Yan the real champ. We'll see if that's true when he meets Sterling in the octagon for the second time.