Only three players have been selected in the NFL supplemental draft since 2013. However, two of those came just last year, and when the league holds the 2019 Supplemental Draft on Wednesday, there's a decent chance at least two players could be selected, one of which could be of interest to the 49ers.
A little background: The supplemental draft is an option for draft-eligible players who did not declare for the regular NFL draft in April. Typically, players who declare for the supplemental draft do so due to unexpected eligibility issues at the collegiate level, such as those related to academics or discipline.