Jackson, who last pitched on Sunday, will still have one extra day of rest, rather than two.
Jackson opened the season with a strong outing in Pittsburgh on April 2, as he allowed just one earned run in 5 2/3 innings. Since then, he has struggled through back-to-back outings in which he's been hit hard: giving up six runs in 4 2/3 innings against the Pirates on April 8 and then allowing runs on eight hits in six innings while taking the loss in St. Louis on Sunday. Control has been an issue, as Jackson has walked 11 in his 16 innings.
Villanueva, meanwhile, is more used to irregular rest as the swing man of the pitching staff. He's made two starts and two relief appearances thus far. After allowing three runs in 6 1/3 innings over his first three appearances, Villanueva gave up nine runs on 10 hits in a blowout loss to the Cardinals on Saturday.
Joe Lemire is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.