"It showed that there was an injury to the UCL ligament," Lovullo said. "That's all I know. I just was told about some of the information a short time ago, and we're still piecing together as much information as possible to come up with the best solution for Taijuan."
Lovullo said he did not know if there was a tear in the ligament. A tear usually requires Tommy John surgery to fix.
"I apologize for being vague, but it's very vague right now," Lovullo said. "Every bit of information that we've gotten is vague. I know in the coming days I'll have more information about what the next steps are."
The immediate next step involved Walker getting on a plane for New York, where he plans on getting a second opinion.
Walker began to experience some tightness in his forearm during the first inning Saturday, and he was examined by a trainer after Yasiel Puig led off the second with a double to left.
Walker remained in the game until the end of the inning, when he was taken out as a precaution. Despite the tightness and drop in velocity, the team was optimistic that Walker would be OK given that he passed the strength tests after he was removed.
"This information came as a surprise to me," Lovullo said of the MRI results. "I thought that he would be OK. It just goes to show you that you can't ever be too safe. I want to believe that he's going to be OK, but he's being examined, and where it takes him from here we're not sure. It's still wide open."
The D-backs will need someone to start in Walker's place Friday against the Padres. The most likely candidates are Triple-A Reno pitchers Braden Shipley and Matt Koch.
"We're still doing some of our own internal work right now about who that will be," Lovullo said. "We feel like we have some real good candidates internally."
Lamb getting closer
Third baseman Jake Lamb, who suffered a left AC joint sprain on April 2, played in an extended spring game Tuesday morning under the watchful eye of Lovullo.
Lamb is scheduled to play third for the first time in an extended spring game on Wednesday.
"Good to be back with the dudes," Lamb said after seeing his teammates for the first time after their 12-day road trip. "I feel great. The shoulder feels great. Now, it's just the baseball stuff -- getting back and making sure that I'm good to go, and not missing a beat when I come back."
That could be quicker than initially expected, if he continues to progress the way he has.
Souza back hitting
Outfielder Steven Souza Jr., who has been on the disabled list since straining his right pectoral muscle during Spring Training, resumed hitting on Monday.
Souza had been shut down for nearly a week after experiencing some discomfort in the pec while throwing, as well as taking a couple of days to tend to a family matter.
"Everything is good," Souza said. "Hitting doesn't bother it, swing feels good and everything in that department is good."
Souza will continue to hit, but likely won't throw again until sometime next week.