If the headaches are determined to be related to a recent concussion, Julien said Gallagher would be held out of the lineup when the Canadiens play at the Ottawa Senators on Saturday (7 p.m. ET; CBC, SN, SN360, CITY, TVAS, NHL.TV).
Gallagher missed four games after sustaining a concussion in a 3-1 loss at the Carolina Hurricanes on Dec. 31. He wore a tinted visor when he returned in a 4-2 loss to the Edmonton Oilers on Thursday, finishing with no points, four shots on goal and two hits in 17:19.
Gallagher reported the symptoms to the Canadiens on Friday morning and did not practice.
"What we're doing with him because he's had a concussion is making sure it's not a relapse," Julien said after practice. "At the same time, it could be a virus. So he's gone to see the doctor and we're being cautious with this situation because of what he's been through.
"If it's concussion-related, then there's no doubt he's out. We're going to always protect the player first before we force somebody like that into a lineup."
Gallagher is second on the Canadiens with 15 goals and tied for third with 32 points. He had an NHL career-high 33 goals last season.
