Horse Sport Ireland announced Thursday that Cathal Daniels has withdrawn his mare Rioghan Rua “for veterinary reasons” ahead of the start of the Olympic eventing competition.

Daniels will be replaced by Austin O’Connor who traveled to Tokyo as the reserve. The Irish team will not incur a penalty for the substitution as it is taking place before the competition begins. O’Connor will ride the 11-year-old grey gelding Colorado Blue whom he owns along with the Salty Syndicate. Daniels and Rioghan Rua now revert to being the reserve combination and can be called upon if required later in the competition if the mare’s veterinary report improves.

“Obviously this is really tough for Cathal and for Rioghan Rua’s owner and breeder Margaret Kinsella, particularly with it happening so close to the start of the competition,” said Irish eventing team manager Sally Corscadden. “We did everything we could and gave the mare every chance to be ready, but unfortunately we were forced to make a decision, and of course horse welfare is always paramount for everyone. Austin now steps in, and he is ready to go. We are very lucky to have someone of Austin’s caliber to step in. He is in great form; we still have a very strong team and are looking forward to the start of competition.”

Eventing dressage kicks off today July 29 at 7:30 p.m. Eastern.