3. Keegan Thompson (bullpen day)
Probably the most likely option would be to do a bullpen day, where Keegan Thompson would probably kick things off. Thompson made 17 starts last year he has gone multiple innings four times this year. Depending on how he pitches, the Cubs would look to get 3-4 innings out of Thompson before handing it over to the rest of the bullpen. Adbert Alzolay has also gone multiple innings, but not since April 11th.
With all the injuries to the starting depth, and Kilian struggling, a bullpen day will save the team from burning an option on either Kilian or Jensen. It will help if Marcus Stroman goes deep into Wednesday's game to save some arms for Thursday, which is likely considering how he has pitched recently (2.29 ERA in 6 starts).