"It's an extended period of time," Mattingly said.
The results of League's recent MRI examination were reviewed Friday by team physician Neal ElAttrache, as well as another doctor. League was diagnosed with posterior shoulder inflammation and prescribed rest.
"I think it's three weeks of rest," Mattingly said.
League would have to build his arm strength after that. He is also expected to pitch in minor league games to get in competitive form.
League pitched in only two games in the exhibition season, most recently March 9.
If League is placed on the 60-day disabled list, he wouldn't count against the team's 40-man roster. That could create an opening necessary to place a non-roster player such as
League, 32, had a bounce-back season last year, posting a 2.57 earned-run average in 63 games. He is in the final guaranteed year of a three-year, $22.5-million contract.
Making his case
Alex Guerrero went into Friday batting .364 with two home runs and seven runs batted in in the exhibition season.
Asked whether he was confident about his chances of making the team, Guerrero replied in Spanish, "What I'm confident about is the work I'm doing and the results I've had. They'll determine if I make the team."
Guerrero has the contractual right to decline a minor league assignment. He has said he would exercise that right and become a free agent if he isn't on the team's opening-day roster.
With Hyun-Jin Ryu starting the season on the disabled list and the
Guerrero has made himself more attractive to the Dodgers by playing multiple positions this spring. He went into Friday having played 18 innings at shortstop, 21 innings in left field and 23 innings at third base.