Chancellor Olaf Scholz's spokesman rejected Mr Johnson's claim that Germany saw it as “better for the whole thing to be over quickly”.
“We know that the very entertaining former prime minister always has a unique relationship with the truth,” said Steffen Hebestreit. “This case is no exception.”
Mr Johnson's reputation for dishonesty was a major factor in his removal from office in July.
“We could see the Russian battalion tactical groups amassing, but different countries had very different perspectives,” Mr Johnson said.
“The German view was at one stage that, if it were going to happen, which would be a disaster, then it would be better for the whole thing to be over quickly and for Ukraine to fold.
“I couldn’t support that, I thought that was a disastrous way of looking at it. But I can understand why they thought and felt as they did.”
Asked about Mr Johnson's comments on Wednesday, Mr Hebestreit briefly switched into English to say they were “utter nonsense”.
He said Germany had swiftly sided with Ukraine by deciding, two days after the invasion, to send weapons to the country.
It marked a historic break with Germany's post-1945 policy of not sending weapons to conflict zones.
However, Mr Scholz's government has been dogged by claims that it has been too slow in providing arms to Ukraine.
While in office, Mr Johnson generally put on a display of friendship with Mr Scholz despite their different political leanings and styles.
In his final phone call with Mr Scholz, he urged the German leader to “stay the course in his political, military and economic support for Ukraine”, Downing Street said.