GLENDALE, Ariz. -- The A’s are not going to risk anything with left-hander A.J. Puk.

Originally scheduled to make the start in Tuesday’s 6-5 win over the White Sox at Camelback Ranch, Puk was held back due to what the club is calling a mild strain of his left shoulder.

An MRI last week, following his start against the Rockies, revealed no structural damage, but the A’s plan to shut down Puk until Thursday or Friday before determining the next step.

“We’re obviously going to be proactive, especially this time in spring,” A’s manager Bob Melvin said. “He’s got a mild shoulder soreness. It’s going to be four or five days that we’re shutting him down and we’ll see where we’re at. Maybe start playing catch after that.”

Puk, the A's No. 3 prospect per MLB Pipeline, who is expected to move into the club's starting rotation this season, looked nearly unhittable in his first two Cactus League outings. The lefty registered two strikeouts over three scoreless innings with a fastball that sat around 95-97 mph. Given the left-hander’s past injury history, including Tommy John surgery in 2018, the A’s want to avoid any potential long-term issue with the shoulder.

The A’s reached into their deep pitching depth and sent Chris Bassitt to the mound for the start. Though the right-hander surrendered a two-run homer on a fastball to Nicky Delmonico in the first, he settled down by not allowing another hit the rest of the way, finishing three innings with two runs allowed on two hits and two walks.

“The first inning I was just trying to establish my fastball. Work it in and out,” Bassitt said. “I think I only threw one off-speed pitch in the first. Just getting a feel for my fastball.”

Heim on fire
The word on Jonah Heim entering camp was that his defense was ahead of his bat. So far, his offensive production is what has been opening some eyes.

Heim, Oakland’s No. 11 prospect per MLB Pipeline, drilled the ball all over the field as part of a 3-for-3 day against the White Sox. He nearly left the yard in his final at-bat, smacking an RBI double off White Sox reliever Carson Fulmer that bounced off the wall in left-center.

In a battle with Austin Allen for the role of backup catcher, Heim’s three-hit day puts him at a .467 batting average through seven Cactus League games.

“He’s swinging the bat really well and he’s pretty good behind the plate,” Bassitt said. “I’m sure we’ll see more of him.”

Machin or Chapman?
An A’s third baseman not named Matt Chapman made a spectacular play at the hot corner. Vimael Machin drew the start in place of the two-time Gold and Platinum Glove Award winner and dazzled with his glove in the first inning. Machin took away a hit from Nick Madrigal as he slid to his left to snag a chopper, spun around and fired a throw over to Seth Brown at first for the out.

“Maybe not a ton of range, but wherever we play him, you hit it to him and he gets his hands on it,” Melvin said. “He’s done a nice job for us.”

Machin is a candidate for the A’s second base job. But as he displayed Tuesday, Machin is also a valuable piece for his ability to play all four infield spots.

Up next
Right-hander Mike Fiers makes his third Cactus League start Thursday in a 12:05 p.m. PT tilt with the Dodgers at Hohokam Park. Fiers is looking to rebound from a rough second outing that saw him allow five runs over two innings against the Reds. Fans can listen to the game live on the A's Cast.