Richards, who has successfully moved into Port's on-ball brigade after initially being cast as a forward, suffered the injury in his career-best game against Fremantle last Saturday.
He collected a personal-best 31 disposals but was sent for post-match scans which revealed a broken index finger.
The Power say Richards will be out for up to a month, adding his name to a lengthy injury list at Alberton.
That group includes captain Connor Rozee - who has played just two games this season after tearing a hamstring tendon and is one of six Power players ruled out for the year - and his deputy Zak Butters.
Butters has returned to the club after ankle surgery and still aims to play again this season, which could be his last at Port as he weighs multi-million dollar offers to return to his native Victoria.
Meanwhile, Adelaide's injury-prone half-forward Luke Pedlar has suffered another hamstring strain which could jeopardise his season.
Pedlar, who has managed just 49 games in six seasons, was hurt in the state league last weekend - his second hamstring injury this year.
"Unfortunately Peds' hamstring does not look to be a low-level strain," Adelaide's fitness boss Ian McKeown said.
"It will require further investigation and discussion over the next several days, however, he will certainly miss some footy."
Fringe Crows backman Hugh Bond also suffered a hamstring strain in the state league and will be out for a month.
And Essendon utility Xavier Duursma will miss the remainder of the season due to a hamstring tear, but teammate Nate Caddy has been cleared to play this weekend.
Caddy was sent to hospital because of an irregular heartbeat in Sunday's win against GWS.
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