Bulldogs supremo Phil Gould confirmed the news on Monday after the former Newcastle forward had scans on the injury sustained in Maori All-Stars camp.
Thompson was a late withdrawal from the All-Stars clash as a precaution after it was initially thought he was experiencing tightness.
The severity of the injury has now been confirmed. The 25-year-old will miss the season opener against St George Illawarra in Las Vegas and the first two months of the NRL season.
Thompson was recruited to give the Bulldogs much needed size and strength up front after they went out in straight sets in last year's finals, having made the top four.
Gould was philosophical about the loss of Thompson when he posted the news on X.
"Not good news for Leo Thompson ... MRI reveals grade three calf tear ... 10 weeks return to play at this stage," Gould wrote.
"It is what it is. We move on. Tough game rugby league."
The Bulldogs had received better news on star playmaker Matt Burton, who left the field in Canterbury's 28-0 trial win over Newcastle.
"Matt Burton MRI scan today shows no tear of the hamstring … Awaiting full report, but appears good to go," Gould earlier posted on X.
"That's a big congratulations to Bulldogs coaches and staff, who saw Matt Burton's reaction in a tackle and ordered him to come from the field immediately."
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