SAN DIEGO -- Fernando Tatis Jr. didn't waste any time showing his usual flair when he started a rehab assignment Monday with Double-A Amarillo.

Playing shortstop and batting leadoff against Frisco, Tatis drew a four-pitch walk in the bottom of the first inning. He then stole second base and scored on a ground-rule double, an encouraging sign for a player who has been out since suffering a left hamstring strain on April 28.

Tatis also gave the hamstring a test when he ran hard to first base after a nubber in front of home plate in the seventh inning and when he collected an infield single to shortstop in the ninth.

The Padres are reticent to put a timeline on Tatis' return, but manager Andy Green gave an indication Monday that the rehab stint could be a short one.

"We just want him to go play baseball and come out healthy," Green said. "If he comes out healthy, swinging the bat well, we'll be looking to get him back here relatively quickly. How quickly he gets back here depends on how he feels, first physically and then timing-wise as a hitter. As soon as those two things click, he'll be back with us in the lineup."

Tatis played the entire nine innings and finished 1-for-3 with two walks and one run scored. He walked on five pitches in the second inning and struck out swinging on a full count in the fourth. He also made a throwing error in the eighth inning.

The 20-year-old Tatis is No. 2 overall on MLB Pipeline's prospect rankings. Expected to start 2019 in the Minors, he instead played his way onto the Opening Day roster and the starting job at shortstop. He slashed .300/.360/.550 in 27 games before the hamstring injury. The Padres were 16-12 after that April 28 game and have gone 14-17 since, entering Monday.