Tapadar was assaulted on the Kalyani Expressway at Jagaddal of North 24 Parganas district, said former state Congress president Pradip Bhattacharya.
The Congress filed a complaint with the chief electoral officer over the attack
"All the attackers were Trinamool men, who were armed to the teeth. I have complained to chief electoral officer Sunil Gupta," he said.
Bhattacharya said Tapadar was also threatened a few days back.
"The administration knows that. But still, they did not make any special security arrangement for him," he said.
7 dead in West Bengal poll violence
Election violence has claimed seven lives in West Bengal and left 740 persons injured in 825 incidents so far, the Election Commission sources said on Thursday.
Over 35 people were arrested in connection to the violence, the EC said.