The 2009 Irish Grand Slam skipper would have become the 10th member of rugby's most exclusive club this weekend if he had played in the British & Irish Lions' third Test against the Springboks in Johannesburg.
But the blows he took to the head in the amazing second Test in Pretoria last weekend has forced him to leave the tour early and miss out on the chance of reaching his century with a seventh Lions Test.
Springboks backs coach Dick Muir said O'Driscolls' premature departure would be an unexpected boost for the world champions as they prepare to make it a 3-0 whitewash of the Lions this weekend.
"Brian O'Driscoll is a class act and had a great Test series. His form in this series highlighted the importance of midfield defence, and definitely forced us to tighten up in that area," said Muir.
O'Driscoll's early departure means Australia's George Smith is likely to be the next player to reach 100 caps when he plays during this summer's Tri Nations Series. He is currently on 99 Tests.
Just behind O'Driscoll in the race to become the first Irishman to reach three figures are prop John Hayes and outside half Ronan O'Gara. Both could be involved with the final test in Johannebsurg and add one more cap to their current totals of 95 and 94 respectively.
WORLD RUGBY'S 100 CAP CLUB
139 George Gregan (Australia)
119 Jason Leonard (England 114 / Lions 5)
118 Fabien Pelous (France)
111 Philippe Sella (France)
103 Gareth Thomas (Wales 100 / Lions 3)
102 Stephen Larkham (Australia)
102 Percy Montgomery (South Africa)
101 David Campese (Australia)
101 Alessandro Troncon (Italy)
99 Brian O'Driscoll (Ireland 93 / Lions 6)
99 George Smith (Australia)
98 Raphael Ibanez (France)
96 Colin Charvis (Wales 94 / Lions 2)
95 John Hayes (Ireland 94 / Lions 1)
95 Chris Paterson (Scotland)
94 Ronan O'Gara (Ireland 92 / Lions 2)