Wales number eight Taulupe Faletau has been sidelined again after an injury blow on his Cardiff comeback.
The 35-year-old made his first appearance since March in the Champions Cup defeat by Northampton on 18 October.
He made an accomplished return but reported finger pain in the days afterwards and will have surgery.
Faletau will miss the United Rugby Championship (URC) derby at Ospreys that finishes the first block of the season.
It is hoped he will be fit to return after the November break for the Nations Championship.
"Unfortunately he had a little bit of a niggle with a pinkie finger, so he will be on the sidelines for a while," said Cardiff head coach Corniel van Zyl.
"He will miss the Ospreys game but hopefully after November he will be fine."
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Faletau has played only 31 times for Cardiff since joining from Bath in 2022 and was limited to seven appearances last season because of shoulder, calf and knee injuries.
"I can imagine he is quite frustrated because after the game he didn't even realise it, then the next day it was sore all of a sudden," said Van Zyl.
"It's a tough one for him to take, but hopefully he can turn it around."
Faletau's lack of game-time meant he was not included in Wales' squad for the Nations Championship, with in-form Cardiff team-mate Taine Basham getting a recall instead.
Wales head coach Steve Tandy said they would not rule out an international return for Faletau, who has won 109 caps and played at three World Cups, but that he needed to show durability to go along with his undoubted quality.
The latest blow only adds to those fears about the legendary number eight, who signed a one-year contract extension with Cardiff last summer.
Cardiff will not only be without Faletau against Ospreys on Saturday, 31 October but their Wales back-row forwards Alex Mann, James Botham and Basham.
They will hope that number eight Alun Lawrence, who has not featured this season because of a number of niggles, will be fit for the trip to Swansea.
Dan Thomas, summer signing Semisi Paea and youngster Lucas de la Rua have played in the back row this season, with hooker Evan Lloyd another option.
Cardiff suffered a third successive loss when beaten by Sharks at the Arms Park on Friday.