I'm not an insider and I do not have 247 premium, so just using deductive reasoning skills. Illinois is/was in on four, 4-star prospects: Brian Robinson, Luke Williams, Marquise Lightfoot, and Ricky Knight. Brian Robinson isn't committed, so he can't be "flipped". Luke Williams is listed as visiting Purdue today. Ricky Knight is listed as visited for Florida State tomorrow, so extremely unlikely he's coming to Champaign the day before.
That just leaves Lightfoot, buuuuuut Werner says it's an official visit. While players now can take unlimited official visits, you are limited to one official visit per school. So whoever it is, it's gotta be someone not reported on here (?).