Dobson is out with an upper-body injury after blocking a shot with his left hand in a 5-2 loss to the Columbus Blue Jackets on April 11.
The Canadiens announced the following day that Dobson would be re-evaluated in two weeks, ruling him out for at least the beginning of the playoffs.
Montreal has managed well in the first round without Dobson, who averaged the third-highest ice time (22 minutes 29 seconds) on the team this season behind Mike Matheson and Lane Hutson.
The Canadiens led the Tampa Bay Lightning 2-1 heading into Game 4 on Sunday night at the Bell Centre.
Dobson, a 26-year-old from Summerside, P.E.I., had 12 goals and 47 points in 80 games this season, his first in Montreal after being acquired from the New York Islanders last summer and signing an eight-year, US$76-million extension.