And his Welsh international colleague Gavin Henson could be the player to benefit from Shanklin's misfortune.
Henson was left out of the original 37-man squad having played little rugby over the past season but he could now be among the contenders to replace Shanklin in this month's tour party.
The 27-year-old toured with the Lions in 2005 but is currently sidelined with an ankle injury he sustained in March.
"I'm a big fan of Gavin," said Lions defence coach Shaun Edwards at the original squad announcement last month.
"I consider him as one of the best defensive players in the world.
"If Gavin can get himself fit and there are any injuries, he will be considered as a replacement."
Henson faces stiff competition from a number of other contenders, however, with McGeechan and his fellow coaches having plenty of options open to them ahead of the 10-match tour of the Republic.
England's Mike Tindall would perhaps provide the most like-for-like replacement for Shanklin, while Newcastle's Jamie Noon may also fit a similar mold.
Max Evans of Scotland could provide some real pace and flair, while Ireland's Gordon D'Arcy could cover both the No12 and No13 shirts.
If the coaches decide to go for versatility, then full back cum centre Delon Armitage could bounce back from his disappointment of missing out first time around.
With only two outside halves in the squad, Welsh playmaker James Hook could even get the call having also played inside centre, while Toby Flood offered similar credentials before injury ended his chances of participation.
When it comes to form players, then how about Flood's Leicester colleague Sam Vesty? Unheralded outside of Welford Road prior to the last three months of this season, Vesty has been in superb form as the Tigers reached both the Guinness Premiership and Heineken Cup Finals.
The 27-year-old has been playing both 10 and 12 for his club and could possibly be a surprise inclusion if McGeechan ignores his lack of international experience.