The 27-year-old is scheduled to see Dr. Timothy Kremchek in Cincinnati on Thursday, the same surgeon who performed A's left-hander Felix Doubront's Tommy John operation earlier this month.
Bassitt was expected to be a key member of the A's rotation this season after impressing as a midsummer addition to the starting staff last year and engaging in offseason workouts with Sonny Gray, even tweaking his delivery to mimic Gray's.
The right-hander posted a 2.79 ERA in his first three starts, performing just the way he envisioned, but his last two starts were less successful. He allowed a combined 13 earned runs across just 8 2/3 innings in that span, showcasing decreased velocity while experiencing progressing pain in his elbow.
• Third baseman Danny Valencia is expected to play in three Minor League rehab games next week before being activated when eligible for Friday's series opener in Baltimore.
Jane Lee has covered the A's for MLB.com since 2010.