Richards sustained the injury during the Bulldogs' 22-point defeat to Geelong last Saturday night.
"Scans have confirmed that this is a moderate grade injury," Bulldogs head of sports medicine Chris Bell said.
"Ed has already started attacking his rehab, with us hoping to get him back in the next four to six weeks."
Richards has starred across half-back this season and joins fellow dashing defender Jason Johannisen on the sidelines.
Johannisen is in the early stages of his recovery from a high-grade hamstring strain that could keep him out of action for up to 10 weeks.
The injuries have opened the door for former Collingwood player Poulter, who joined the Bulldogs' VFL side this year and was given an AFL career lifeline at the mid-season draft.
Laitham Vandermeer and Hayden Crozier are also in the mix to replace Richards.
Bulldogs premiership hero Toby McLean is set for a stint on the sidelines after suffering some acute lower back pain after he was tackled in the VFL over the weekend.
"He has an area of bone overload in his back that will need some time to settle," Bell said.
"Once his acute pain improves, we will confirm his return-to-play plan, but expect him to miss some footy over the next month."
Bulldogs captain Marcus Bontempelli (knee) and fellow midfielder Adam Treloar (calf) have been given the all-clear to play against Port Adelaide on Friday night despite injury concerns in the Geelong clash.
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