There's no word yet on which four RAW Superstars will be appearing on tonight's SmackDown episode under Vince McMahon's new WWE Wild Card Rule, but we know of several blue brand Superstars who will not be appearing on the show.
Aleister Black, Apollo Crews and Elias are among the Superstars who left with the RAW roster earlier today for the first leg of the European tour that kicks off this week, according to PWInsider. They will not be appearing on tonight's SmackDown episode. As Raj noted earlier, Roman Reigns also will miss tonight's SmackDown due to being booked on the tour. He left out earlier today with Black, Crews, Elias and the RAW roster.
These four Superstars are touring with the red brand because their scheduled were locked in before the 2019 Superstar Shakeup. The new WWE Wild Card Rule now gives them a cover for being there.
We don't know if WWE Intercontinental Champion Finn Balor flew to Europe this morning, but he is still listed for a match against Elias at Wednesday's live event in Belfast. It's possible that plans changed and they kept Balor back for SmackDown.
On a related note, WWE still has Sasha Banks listed for the Belfast show on Wednesday, the first event of the tour, but that appears to be an error because she's not listed for any other event on the tour, and she's not on the card for Wednesday's event that is going around locally. WWE also has Bayley listed for Wednesday's event, with Banks, but that appears to be another error because she is scheduled for tonight's SmackDown.
Most of the RAW roster will be unable to appear on tonight's SmackDown because of the European tour that kicks off on Wednesday and runs through Friday, May 17. WWE United States Champion Samoa Joe, The Usos and AJ Styles could appear on tonight's SmackDown because they are booked for blue brand live evens on the tour. AJ teased on last night's RAW that he could appear with "some friends" on tonight's SmackDown, indicating a possible appearance by The Club - Styles, Luke Gallows and Karl Anderson.