Trumbo was evaluated at the Kerlan-Jobe Medical Center in Los Angeles, and tests performed there revealed the fracture.
The 25-year-old was taken out of Saturday's game against the Oakland Athletics with what was termed as right ankle discomfort, and was also removed from Sunday's contest with the same problem.
He will be re-evaluated in 4-to-6 weeks.
The Angels are still mathematically in the AL wild-card chase, being three games behind Boston with three games remaining, The Halos finish their year by hosting AL West champion Texas.
LA's late-round pick in the 2004 amateur draft has made an impression this season, staking a claim for rookie of the year in the AL by hitting .254 with 29 home runs, 31 doubles and 87 RBI in 149 games.