Arrieta was placed on the 10-day injured list with a right thumb abrasion Tuesday, Russell Dorsey of the Chicago Sun-Times reports.
Arrieta was lit up for seven runs in just 3.1 innings of work his last time out against the Reds. It's possible the thumb issue was at least partly to blame, as he'd pitched to a 2.57 ERA across his first five starts. The veteran will be eligible to return May 14, though it's not yet clear whether he's expected to do so. The Cubs have three off days before then, so they may be able to get by without an extra starter if his absence is brief, though they'll call on Keegan Thompson for the nightcap of a doubleheader against the Dodgers on Tuesday.