Russia’s invasion has pommeled Ukraine‘s cities and laid low some of the country’s best known exports, from its grain harvests to the sports it excels at, like boxing.

The morning after Russia invaded Ukraine, Dmitry Sosnovsky, a storeyed national boxing coach, gathered with 15 boxers and trainers in their gym here to decide what to do.

Some would join the armed forces, some became refugees and others, like Mr. Sosnovsky, decided to aid the fight in other ways. None gave a thought to boxing, a sport that Ukraine has long excelled at on the international stage.

“For this generation of fighters there will be a gap,” said Mr. Sosnovsky, who has coached many of the country’s best boxers, including, at one time, current heavyweight world champion Oleksandr Usyk. “But we will restore it,” he said.

Russia’s invasion has pommeled Ukraine’s cities, killed thousands and turned millions into refugees. It has also laid low some of the country’s best known exports, from its grain harvests to the sports it excels at, like gymnastics and boxing.

Usyk, who holds three of the four main heavyweight belts, is set to make a high-profile return from a stint in the Ukrainian army on Aug. 20, when he will fight Anthony Joshua, the British fighter he took the titles from. The fight in Saudi Arabia will be shown free of charge in Ukraine, a sign of its importance for the embattled country.

With the war ongoing, the long-term impact on the rest of Ukraine’s boxing world has yet to be seen. At the Andriy Kotelnik Academy of boxing in Lviv, in western Ukraine, Mr. Sosnovsky believes a negative impact is inevitable.

Before the war, around 100 trained at the gym here, in the base of a Soviet-built apartment block. Now there are around 35 to 40 that train, Mr. Sosnovsky said. Eight of the gyms’ boxers are fighting on the front line.

Vyacheslav Senchenko, a former world welterweight champion who now trains boxers in Kyiv, said many of his fighters have told him they are quitting the sport, saying they need to look after their family or earn money in a job.

It is the boxers just starting out that Mr. Senchenko says he feels most for, given there are currently no professional or amateur fights in Ukraine. Young men are also not allowed by law to leave the country.

“There is no opportunity for younger guys to achieve real fighting experience,” he said.

Since the war started, eight Ukrainian boxers, who had won titles at a national or regional level, have been killed in fighting, including a former European youth champion, according to a government website.

Mr. Sosnovsky says the damage to the sport isn’t just about casualties and missed training opportunities. The country’s entire boxing infrastructure has been degraded.

Fourteen sports facilities have been damaged and three destroyed, according to Ukraine, Ukrainian government. Trainers and boxers have had to leave their gyms and equipment in occupied territories. Mr. Sosnovsky said a friend who is a boxing coach fled from Mariupol, a port city now in the hands of Russia, and ended up in Germany.

“He is a world class trainer, and he has to start again from zero,” he said.

The effects of the war are being felt across all sports here.

Olga Shulpina, a gymnastics coach at a children’s sports school, took their athletes and parents to a camp in Poland this summer and is now unsure how many will return.

“It is difficult to predict how many promising personnel will be lost for Ukrainian sports in the coming years,” she said.

One of Ukraine’s largest fencing centres was destroyed in an attack on the city of Kharkiv. Andrey Makarushchenko, who ran the centre and is president of the regional fencing federation, said the loss will have a serious effect on fencing training in the country.

All soccer competitions, including the country’s main professional league, were stopped when the war started. The country’s national side regrouped to compete in the playoffs for a coveted spot in this year’s soccer World Cup, only to suffer a narrow loss to Wales in June.

In recent decades, the country has particularly excelled at boxing.

Brothers Wladimir and Vitali Klitschko dominated the heavyweight division from around 2004 to 2015. Vasiliy Lomachenko won titles in three weight classes and Andriy Kotelnik was a former lightweight world champion trained by Mr. Sosnovsky and who owns the Lviv gym. When the war began, Mr. Lomachenko, like Mr. Usyk, joined Ukrainian forces.

With Mr. Sosnovsky as head coach, Ukraine topped the medals table at 2011’s amateur World Boxing Championship and were second at the 2012 Olympics to the U.K., the games’ hosts.

Mr. Sosnovsky keeps in regular contact with the boxers he trains who are now on the front line. When they arrived there, several called to say they were under equipped.

“‘We need socks, bulletproof vests, radios,’” Mr. Sosnovsky said they asked.

The 64-year-old, who was born in a Russian Arctic penal colony that his mother had been sent to, made several trips to bring equipment to the front line.

The gym’s weight room is currently being used to sleep several refugees from eastern Ukraine. At one point there were up to 40 sleeping on its floor.

On a recent morning, only one fighter trained, the sounds of his skipping echoing through the empty gym. But the 17-year-old middleweight prospect is also soon set to leave, immigrating to Poland with his mother.

“For the school, he will be lost. He will … probably be a Polish boxer,” said Mr. Sosnovsky, who has trained him for the last five years.

Mr. Senchenko, the former welterweight champion, said that of five professional fighters he helps coach that he rates as promising, two are now in Germany.

Matviy Bulyk, Mr. Sosnovsky’s fighter, says he doesn’t want to leave the country and hopes to always compete under a Ukrainian flag.

“But I have no say in the decision,” he said.

Before each major international fight Mr. Sosnovsky used to motivate his boxers while sending them into the ring by telling them they were fighting for their family and country.

When boxers head for the front line, he repeats the same message.

“Now, you’ll fight for your father, for your mama, for your country,” he said.

—Katia Rudeshko contributed to this article.

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