After immediately coming out of the game, Lucas had an X-ray, which showed a non-displaced fracture.
Now that Lucas will open the season on the disabled list, Donovan Solano will rejoin the team hours after he officially was optioned to Triple-A New Orleans.
Lucas and Solano were in competition for the utility infield spot.
"It's sore," Lucas said.
Lucas and the Marlins initially were hopeful that the injury wouldn't be serious.
The Marlins rallied with five runs in the eighth inning. During the rally, Lucas was pegged by a McGregor pitch. He was checked by trainer Sean Cunningham and immediately replaced for a pinch-runner.
Earlier in Spring Training, Lucas missed about a week due to a strained left hamstring. He has impressed since his return.
The final days of Spring Training are always reason for concern regarding freakish injuries.
"These last three days are torture," manager Mark Redmond said. "You're trying to get the guys through it. At the same time, too. Some of those guys you're trying to get at-bats for, especially, your role players. We hope everything is all right."
Joe Frisaro is a reporter for MLB.com. He writes a blog, called The Fish Pond. Follow him on Twitter