Around 20,000 volunteers from around the world signed up after Ukrainian President Volodymyr Zelenskyy called for foreigners to fight with Ukrainians.
Matthew, a British veteran who served two tours in Afghanistan and is now helping train fighters in Ukraine, told The Times of London that Russian forces appeared to be inferior to the Ukrainians.
Matthew told the paper that he saw a group of Russians enter the city of Irpin, which is located near the city of Kyiv. He said that most of the Russian troops were killed.
Matthew said that the Taliban would do a better job.
Matthew told the paper that he is not part of the foreign legion but is training civilians who have joined the territorial defense forces.
The veteran told The Times that he believed he was 100% on the winning side after seeing Russian troops in Irpin.
They are tactically inferior. He told the paper that they had taken a lot of ground from the Russians.
Matthew asked if any of the 50-strong Ukrainian force had been shot at before, and none of them had. He said they appeared to be more capable than their Russian counterparts despite their inexperience.
The Russian military has made slow progress since launching its invasion of Ukraine.
Russian President Vladimir Putin thought his military could capture Kyiv in two days.
Reports say that the Russian military has lost many top officers.
More than 15,000 Russian troops have been killed by the Ukrainians. Up to 7,000 Russian soldiers have been killed according to the Pentagon.
The scale of the losses has not been acknowledged by the Kremlin.