Motlop, 27, had surgery on Monday night after being kicked in the ankle in Saturday night’s 93-point loss to the Western Bulldogs at TIO Stadium in Darwin.
Last month, the freakish forward missed two weeks with an unrelated injury to the same joint.
The news comes as a major blow for the Power, who are already without vice-captain Shaun Burgoyne, Chad Cornes, Travis Boak and Matt Thomas.
Burgoyne has not played since suffering bone bruising to his knee against Melbourne in round three and the club has not put a timeframe on his return.
Tall forward Justin Westhoff also missed eight weeks earlier in the season after breaking a bone in his foot.
Port Adelaide midfielder David Rodan said it was almost impossible to replace the likes of Motlop, Burgoyne and Cornes.
“It’s pretty tough. You always miss your key players when they’re injured and this year we’ve had Daniel, Shaun and Chad out,” Rodan said.
“They are all very key players for us, but it does provide a good opportunity for some young players to come in. I think (first-year player) Matthew Broadbent has been talked about for a fair while and he’s playing some good footy.
“Hopefully, Nathan Krakouer will get a recall too, so we’ve got plenty of players to call upon.”
Of the players who missed the trip to Darwin, only full-back Alipate Carlile (virus) and impressive draftee Hamish Hartlett (hamstring) are expected to be fit for the clash with Geelong at Skilled Stadium on Saturday June 28.
Port Adelaide was flying over the pre-season, with few players spending meaningful time on the sidelines. Rodan said his side’s current build-up in the medical room was a result of sheer bad luck.
“They’re not little injuries. They’re all big ones and they’ve been to key players as well. We understand that happens, but hopefully later on in the year those guys can come back and make a real impact,” he said.
