Messi has not played in any of Barcelona's four LaLiga matches since suffering the calf injury in pre-season. Ernesto Valverde has preached caution with Messi, insisting he wouldn't rush the captain back and risk further time on the sideline.
In an interview with SPORT last week, Messi called the injury "really bad because it happened on my first day back [after the Copa America] and it originally looked to be something minor but, in reality, I have been out of action for the past 15 days.
"Now I know what it is and I feel more at ease. I will return when I feel I have fully recovered.
"I've spent a long time on the sidelines. As soon as I started this happened to me and I can’t wait to return."
Barcelona open their Champions League campaign on Tuesday at fellow Group F favorite Borussia Dortmund.