Conor McGregor posed with Putin after being invited to the 2018 FIFA World Cup in Russia as his guest.
In 2018, the Crumlin fighter hailed Russian president Vladimir Putin as "the greatest leader of our time" after they met at a sports event.
Tensions are extremely high in Europe after Russia launched a military attack on Ukraine on Thursday morning.
Mr Putin, in a statement on Russian TV overnight, warned allies of Ukraine who try to interfere with his attack will "face consequences greater than any you have faced in history".
It has seen bombs and soldiers entering the Ukraine all morning, with at least 40 people killed so far.
The 'Notorious' posed for a photo with the Russian leader but was told as he did so not to put his arm on Mr Putin's shoulder.
A clip of the meeting was shared on McGregor's Mac Life website at the tiHe later uploaded pictures on Instagram and described Mr Putin as "one of the greatest leaders of our time".
He posted: "Today I was invited to the World Cup final as a guest of Russian President Vladimir Putin.me.
"This man is one of the greatest leaders of our time and I was honored to attend such a landmark event alongside him.
"Today was an honour for me Mr. Putin. Thank you and congratulations on an amazing World Cup."
He said: "The UN Charter requires all countries to refrain from the threat or use of force against political independence and territory of any state. Today's use of brute force is a serious affront.
"It presents Europe with the most grave security situation it has faced in decades, with repercussions for global security. It cannot and will not go unanswered.
"President Putin will be held accountable. This evening I will join with our partners in the EU to adopt the most severe package of sanctions we have ever considered, on top of the measures already announced. They will be aimed to hit Putin and his henchmen where it hurts most."
