The injury only came to light when the South African saw a specialist on Monday
Irish giants Munster have been forced to change their plans to add former South African Under-20 captain CJ Stander to their European Cup squad.
The Irish province confirmed that they have instead added James Coughlan to their squad, as permitted under competition rules.
Stander, who was first choice fill that slot, has been omitted after suffering a fracture in his right hand in the 31-3 Pro12 win over Glasgow Warriors at the weekend.
He ruled out for a month by the injury. The former SA U20 captain sustained the injury after scoring two tries on his first Munster start against Glasgow last Saturday.
The injury only came to light when the South African saw a specialist on Monday and he is expected to be out of action until January.
Coughlan was omitted from the original squad, after suffering a torn groin in a Pro12 match in September. At that time the prognosis was for a five-month recovery period.
However, Coughlan who was particularly diligent about his rehab has returned to action way ahead of schedule to be registered ahead of the midday deadline on Wednesday.
Ivan Dineen who was registered in place of Coughlan back in September, is now de-registered as per competition rules.
Munster are also set to be handed a massive boost ahead of their crucial back-to-back European Cup clashes against Saracens, with scrumhalf Conor Murray confident of being fit for Saturday's Round Three showdown at Thomond Park.
Unbeaten Saracens top Pool One with nine points, three clear of former double European Cup champions Munster, with a home win vital for the Irish team's hopes of qualifying for the prestigious knock-out stages.
Murray was absent when Munster beat the Warriors last weekend after a knee injury sustained last season flared up again.
The international scrumhalf suffered a small tear in the Six Nations game against France last season and a heavy playing work load aggravated the injury.
"It's only a small thing," he said.
"The week off did it the world of good. I feel relaxed and I came through my first pitch session and it feels fine."
But Munster may well have to face Steve Borthwick's Saracens without hugely influential lock Paul O'Connell, who was restricted to indoor training while Murray was taking part in the pitch action.
* Meanwhile Cardiff Blues have been dealt a triple blow ahead of their European Cup tie with Montpellier.
The Welsh region go into the "must-win" Pool Six clash without Welsh internationals Leigh Halfpenny, Bradley Davies and Jamie Roberts.
Halfpenny will see a specialist this week following the neck injury he suffered while on international duty against Australia.
The fearless fullback was stretchered off in a neck brace and taken to hospital after a sickening collision in the clash.
He was kept overnight before being released with no serious injury on Sunday, but it is unknown when he will be able to return to action.
Davies continues to be assessed with weekly neurological tests following the severe concussion he suffered at the hands of Andrew Hore.
And Jamie Roberts hyper-extended his left arm during Saturday's defeat to the Wallabies and had been ruled out of the Arms Park encounter.
"We are not expecting any of them to be involved this week," said Blues backs coach Gareth Baber.
"Leigh is seeing a specialist this week. How long he will be out for I am not exactly sure.
"Bradley is seeing a neuro-specialist and they are monitoring how he reacts to tests.
"There are no long-term worries that we know of. He has taken a smack to the face. In the first two weeks, you've just got to let things settle down a little bit.
"Jamie hyper-extended his arm. He's had an MRI scan and we are monitoring him and seeing how he is.
"The guys have had a tough series. That's the nature of the game we play.
"When they play for Wales, you want them to play with their heart on their sleeve and really go for it.
"It is frustrating, but that's what we deal with," he said.
"This is what we have got. There is quality in the squad and they are going to have to step up and play against Montpellier."
The Blues are already without back-three trio Dan Fish, Tom James and Chris Czekaj and Baber admits it is a concern.
"We have issues and they don't go away," added Baber.
"This is the business and we have to try and squeeze as much as we can out of the players that take the field.
"We've just got to deal with it and crack on and plan for the weekend."
The Blues need to beat Montpellier home and away to maintain their slim hopes of reaching the quarterfinals.