The Argentine was rushed back to face Bayern on Tuesday and put in a toothless performance as Barcelona lost 4-0 at the Allianz Arena
The Argentine's participation in the Allianz Arena clash had been in doubt right up until just a couple of hours before kick-off, with the 25-year-old having failed to feature for the Blaugrana in all but one game since sustaining a hamstring injury against Paris Saint-Germain on April 2.
The Catalans eventually slumped to a 4-0 loss, with Messi putting in a disappointing performance and Minguella believes he was not fit enough to feature.
"His father told me at lunch that he was not able to play," the agent-turned-pundit is quoted as saying by Marca.
Barcelona will be hoping that Messi is fully fit when they meet Bayern again in the second leg at Camp Nou on May 1 as they look to produce an unlikely comeback.
Barcelona travel to Athletic Bilbao on Saturday.