Connecting to Modem with Ethernet cable directly to my PC....can this be done or do I need a router?

Not very tech savvie.  Have Comcast voice & date modem for home.  Use for wifi connection to PCs and printer and fo telephone.  Have to work at home.  Need to hard wire my PC.  Can't use wifi.  Can I plug Ethernet cable directly from my PC to the Comcast voice and data modem or do I need to adda router???  I don't want to do anything until I can be sure.  Calling Comcast directly has been a lost cause.  Can anyone please advise?   Thank you.