Arunachal Pradesh shooter Tamang shot into limelight after clinching the 25-metre rapid fire pistol gold at the 2006 Commonwealth Games in Melbourne.
Vijay, who rushed 33-year-old Tamang to Batra Hospital here, said his friend was in serious condition.
"Pemba tamang in serious condition, took him to batra hospital. 'Get well soon'," Kumar wrote on his Facebook page.
"Pemba got viral fever and cold, glucose bottle on. Took blood for testing, don't worry guys will save him. We are eye witness," he added.
Tamang had won the centre fire pistol gold with a score of 582 in the Sahara 56th National shooting championship last year.
In 2010, Tamang was in the news when he was stopped by immigration officials in Mumbai from boarding a flight to Beijing as his passport had the "invalid" stapled visa, which China issues to Indians from Jammu and Kashmir and Arunachal Pradesh.