The Bruins called up defenseman Urho Vaakanainen from Providence of the American Hockey League. The 19-year-old will make his NHL debut against the Canucks.
McAvoy leads Bruins defensemen with six points (one goal, five assists) in seven games.
"McAvoy yesterday said he wasn't feeling right so we contacted our medical staff back home and he's on a plane today to undergo some tests," Bruins coach Bruce Cassidy said. "It's a vague answer because I don't know what is going on. Charlie just said he wasn't feeling right so we wanted to make sure he gets looked at."
Miller blocked a shot with his hand during a 3-2 overtime loss to the Edmonton Oilers on Thursday.
"We'll know in a few days what the X-ray shows and whether they cast it or he has to miss time," Cassidy said.
The Bruins have lost two straight after winning the previous four.
Goalie Jacob Markstrom starts for the Canucks, who are 3-1-0 in their past four games.