Walker (elbow) threw a 39-pitch simulated game Tuesday, Richard Morin of the Arizona Republic reports.
The right-hander came out of the session healthy but was not pleased with his command. "I was just a little erratic, a little wild," Walker said. "A lot of walks, getting behind in counts. Just not where I expect myself to be, but I'm also being a little hard on myself. It'll get better as we go." Walker's fastball was estimated to be in the low 90s, which he feels will improve as he builds arm strength. A midsummer return is still the expectation.