The skipper told essendonfc.com.au despite the setback, he is still on track for the first round of the home and away season.
"I got a corky yesterday during training and this morning I woke up with a bit of knee soreness, so We decided to get a scan and unfortunately I have a grade one lateral strain of the ligament," Watson said.
"I suppose in knee terms it is insignificant. I won't play in the opening round of the NAB Cup but should be fine for the second game in Wangaratta.
"It is more of an annoyance really but you have to respect the injury."
Watson's injury doesn't require surgery and he will be able to continue pre-season training.
Essendon will face both Collingwood and the Western Bulldogs in the opening round of the NAB Cup.
