We may finally have an explanation for Chris Sale’s lousy April.

The ace left-hander, who’s struck out at least 10 batters over his last four starts, started the season with a greatly diminished fastball and inability to put hitters away. It was theorized Sale was possibly still dealing with the aftereffects of the shoulder injury that sidelined him for the bulk of the second half of last season, even though the Red Sox had just inked him to a five-year, $145 million extension.

As it turns out, Sale was dealing with an injury, but it had nothing to do with his shoulder or arm. He was battling a previously undisclosed toe injury, according to the Athletic’s Jen McCaffrey, which impeded his Spring Training.

“Chris’ spring training was different,” Red Sox pitching coach Dana LeVangie told McCaffrey. ““We tried to do the exact same things we did last year. The only difference is, Chris was going through contract negotiations, (but) he had a little bit of a toe injury that slowed him down a little bit, so there were some things that led up to the early-on stuff. I basically felt like he was going through his spring training, sort of in April.”