The discovery was made while Artyom Sidorkin, 28, from the Urals city of Izhevsk, was undergoing surgery.
Sidorkin had complained of extreme pain in his chest and had been coughing up blood, doctors suspected cancer.
"I blinked three times and thought I was seeing things," Izhevsk surgeon Vladimir Kamashev told the paper.
Medical staff believe Sidorkin had somehow inhaled a seed, which later sprouted inside his lung. The spruce, which was touching the man's capillaries and causing severe pain, was removed.
"It was very painful. But to be honest I did not feel any foreign object inside me," Sidorkin said.