Hamilton was claimed off waivers from the New York Mets on Monday. Hamilton, who turns 30 on Wednesday, went 1-for-22 in 17 games with New York before he was designated for assignment on Friday.
Martinez, an infielder/outfielder, is 0-for-14 since coming over in a trade with Tampa Bay on Aug. 30. The Cubs were hoping he could help address their trouble against left-handed pitching this year, but it hasn't worked out so far.
"In this weird season it's hard to give somebody consistent at-bats when they feel off and their timing's off," manager David Ross said before Tuesday night's series opener against Cincinnati. "So just giving him an opportunity to go down there, get regular at-bats, get his timing back and come back and be the guy that we really need."
Right fielder Jason Heyward was out of Chicago's starting lineup for the second straight day. Heyward left Sunday night's 7-3 loss to St. Louis because he was feeling lightheaded and having difficulty breathing,
Ross said Heyward underwent more tests on Tuesday. Heyward has been one of Chicago's most consistent players this year, batting .300 with five homers and 17 RBIs in 35 games.
"Talked to him a little bit this morning. Still feeling a little bit fatigued," Ross said, "so I'm going to stay away from him to start the game for sure."