Upton suffered a hyper extension of his left big toe during what initially seemed like a minor collision with the outfield wall at Angel Stadium on Sunday. He was sent for imaging the following day and the Angels had the results reviewed by three different doctors throughout the week.
The timeline, as revealed by Angels manager Brad Ausmus before Friday's road game against the Oakland Athletics: 8-12 weeks.
"We were hoping for a shorter recovery," Angels general manager Billy Eppler said, "but this is what it is."
Upton's absence leaves a significant void in an Angels lineup that will also be without Shohei Ohtani at least through the month of April.
In the meantime, the Angels will deploy a platoon of Peter Bourjos and the recently signed Brian Goodwin in left field. They have used Justin Bour in the No. 3 spot behind Trout for their first couple of games, which Upton has watched from home in a walking boot.
Eppler said he had the flexibility to eventually acquire outside help but doesn't see anything presenting itself so early in the season.
"Right now," he said, "we're going to go with the guys we have."
Upton, who has four years and $90 million remaining on his contract, has been steady throughout his career, playing an average of 152 games from 2011 to 2018. Last year, in his first full season with the Angels, the 31-year-old hit 30 home runs and sported an .808 OPS, trailing only Trout and Ohtani for the team lead.
Jo Adell, widely considered one of the brightest prospects in the industry, was on track to potentially be major league ready by the end of this season. But he suffered a sprained left ankle in spring training that was initially expected to keep him out until June.
Upton is currently doing range-of-motion exercises and physical therapy. He will be out of the boot in four weeks, at which point he can begin the process of working his way back.
"You lose a middle-of-the-order bat for a little while, that obviously is going to have an impact on your run production," Eppler said. "But we still have a lot of really talented hitters in this lineup."