Walker (elbow) had a 20-pitch bullpen session Tuesday, Steve Gilbert of MLB.com reports.
The throwing session was Walker's first since undergoing Tommy John elbow surgery in April of 2018. "Obviously, it's been a long, grinding process, and these are when you start to see some really good moments for these guys, a smile on their faces. I think it was a good day for Taijuan," said manager Torey Lovullo. Walker will slowly ramp up over the next few months and could be an option for the Diamondbacks after the All-Star break.