Swisher is on the 15-day DL with a hyperextended left knee. Santana is on the 7-day DL with a concussion, which was caused by a foul tip off his mask while he was catching on Sunday. Swisher might be back sometime during the Tribe's 9-game road trip that begins next weekend. Santana could be back on Monday for the team's series-opener against Boston.
Both players' numbers have been way down this season. Swisher has a line of .211/.312/.319. His power is way down, as he's hit only 3 home runs, after hitting 20+ in each of the last nine seasons. Santana's line is .159/.327/.301, due in part to to a .177 BABIP (though some of that is due to a lower than usual line-drive rate). Santana just had a great four game-series against Baltimore, with a home run, two doubles, and six walks, and I consider him the bigger loss of the two players.
Jesus Aguilar and George Kottaras have been brought back up from Columbus to take their roster spots. Aguilar will likely start at first base at most games, while Kottaras will serve as backup catcher. (As soon as Kottaras plays, he will lose his spot on the team's all-time greatest one-game wonders.)
Because Kottaras was not on the 40-man roster, relief pitcher Blake Wood has been designated for assignment. He'll be placed on waivers, and if he clears them, he can stay with the organization.