Beckett injured the thumb nearly two weeks ago in the Dodgers' spring training clubhouse when he was reaching for the handle of a door and someone pushed it open from the other side.
"You know how it says, 'Out,' and, 'In?' Somebody came out the 'In,' " Beckett said. Asked who the other person was, Beckett said, "I'm not going there."
Beckett is lined up to be the Dogers' fifth starter and he said he still has enough time to take his place in the rotation when the season starts. The Dodgers, who open their season March 22 in Australia, won't need a fifth starter until mid-April. Beckett is coming off surgery for thoracic outlet syndrome, but he has had no setbacks in the area of the surgery.
The team signed Paul Maholm as a backup in case Beckett isn't healthy enough to pitch.
"It's frustrating, but it could have happened at a worse time," Beckett said.
Beckett allowed just one hit in three innings, holding the Cubs scoreless, but he experienced pain when he tried to throw his curveball.