The Pirates released Tilson on June 9.
Tilson, who is a long shot to make the team out of camp, hit .167 in 18 Grapefruit League at-bats.
Tilson agreed to a minor-league deal with the Pirates that includes an invitation to spring training, Adam Berry of MLB.com reports.
Tilson elected free agency rather than accept an outright assignment to the minors, James Fegan of The Athletic reports.
Tilson was outrighted to Triple-A Charlotte on Thursday.
Tilson was optioned to Triple-A Charlotte on Thursday, James Fegan of The Athletic reports.
Tilson is out of the lineup for Sunday's game against the Athletics, Daryl Van Schouwen of the Chicago Sun-Times reports.
Tilson will start in center field and bat eighth Sunday against the Cubs.
Tilson (illness) is back in the lineup Friday, starting in center field and batting eighth against the Twins.
Tilson left Wednesday's game against the Red Sox with flu-like symptoms.