OAKLAND -- Already, the A's fifth-starter competition is down a candidate less than a week before camp opens, as right-hander Daniel Mengden underwent right foot surgery on Wednesday.
Mengden fractured a bone just below his right big toe while throwing a bullpen session at his home in Houston on Jan. 31, the A's announced. He is expected to be in a walking boot for six weeks, and there is no timetable for his return.
Mengden, who will turn 24 this month, was considered a top contender among many vying for a job in the A's rotation. He could still factor into their plans midseason, but he'll undoubtedly be precluded from the Opening Day starting five.
By subtracting Mengden from the mix, it's fair to assume a rotation of Sonny Gray, Kendall Graveman, Sean Manaea, Jharel Cotton and Andrew Triggs, barring injury. But Oakland's pitching depth remains bountiful, and several others hope to push their way into the conversation, including Frankie Montas, Jesse Hahn and Raul Alcantara, among others.
In addition, Tommy John-rehabbing patients Chris Bassitt and Felix Doubront could also factor in the picture when they're fully recovered.
Mengden, who came to the A's in the Scott Kazmir trade in 2015, made his big league debut last season, after beginning the year with no experience above the Class A level. He went 2-9 with a 6.50 ERA in 14 starts over two stints with the A's, striking out 71 batters in 72 innings.
Jane Lee has covered the A's for MLB.com since 2010. This story was not subject to the approval of Major League Baseball or its clubs.