Rabbi Mendy Cohen, 39, has been a Chabad emissary to the Ukrainian city of Mariupol for 16 years.
A private plane brought Cohen to Israel after he was infected with the coronavirus and became seriously ill.
Cohen did not have any preexisting conditions and was healthy when he was infected.
"My blood oxygen dropped suddenly and since then the deterioration has been rapid," said Cohen to Ynet. "At least 150 Jews died in Ukraine. The medical situation there is so difficult. Doctors give patients' families a list of medicines, and they have to buy them themselves."
Cohen warned that there is a large outbreak in Ukraine and doctors are struggling to keep up with the load.
"It is less recommended coming, it is a big danger," said Cohen. "This is the fourth week I have been receiving treatment, only now I am starting to feel better, but not everyone can afford such a flight."
"People who travel to Ukraine, to Uman, do not understand that this is a crazy danger to lives," stressed Cohen. "There are no conditions. I think I now have a mission to stand at the gate and warn, to save lives."
Rabbi Avraham Wolf, a friend of Cohen's and the rabbi of Odessa, joined Cohen in encouraging pilgrims not to come to Uman.
"The state has banned access to Uman, and anyone intending to do so is at risk of coronavirus. I can not tell the hassid not to come to the Rebbe, but as someone who knows the medical system here, the place and the residents, this is the reality on the ground," said Wolf to Ynet. "The health care system has completely collapsed. Whoever comes here makes a dangerous, fateful decision. Do not do this."A ministerial team in Israel began working last week to organize a plan to allow a limited pilgrimage to the grave in Uman. It is unclear if a lockdown in Israel would lead to the cancellation of such a plan.
Wolf warned that there is not "a single room" available in Odessa, and they've run out of equipment to treat coronavirus patients. "Ukraine is in a place that Israel is afraid to reach - the collapse of the health care system. It's impossible to help anyone," said Wolf.
"This is happening in Odessa, the second largest city in Ukraine. In small places the situation is much worse," added Wolf. "Every day we hear about dozens of people who are sick in Corona, who are sent home because there is no way to help them."
"We did not think he could take it so hard because he does not fit into any category and is not in a risk group," explained Cohen's wife, Esther. "We thought it would pass very quickly. I was sure that when he went to Odessa to be hospitalized, it was just to be safe. We were sure he would be released and then his condition began to worsen."
Wolf explained that the president of Ukraine asked him two weeks ago if a letter by the rabbis in the area would help convince the Breslov hassidim not to come.
"It should be understood that for Breslov hassidim coming to Uman is like me telling you not to circumcise your son on the eighth day," added Wolf to Ynet. "We can understand that. We can not tell them not to come. We need to raise awareness and tell them what is happening here."
A clinic set up by the Jewish community in Odessa is currently able to handle 35 patients in serious condition. $350,000 in donations has been invested in the clinic.
In the meantime, volunteers and emissaries are working to provide aid to the Mariupol Jewish community ahead of the High Holy Days. Food packages are being distributed to those in need in the community of several thousand Jews. Before he left Ukraine, Cohen worked to provide coronavirus tests, blood pressure monitors, mental support and medical aid for the Jewish community.
"My message is that life is more important than anything, and you have chosen life," stressed Cohen to Ynet. "We will have many opportunities to visit and travel, to keep life that message."