The slugging first baseman will miss his third straight game Tuesday night as the Rangers open a two-game home series against the Mariners and their locked-in right-hander.
Fielder, who sat out Saturday and Sunday with an ongoing disk problem in his neck after receiving an injection, was on the original lineup posted for Tuesday night's game against Seattle. But he was then scratched more than three hours before the game after taking some swings.
"We've had to deal with adversity all year," said Mitch Moreland, who has played first base the last three games. "You come in every day ready to play."
Moreland hit a two-run homer in Sunday's 6-2 win over Toronto to help the Rangers (21-23) snap a four-game skid.
The Rangers have won seven of 10 against the Mariners (21-22), including three of four at home April 14-17. But they didn't face Iwakuma (2-0, 1.59 ERA), who has been impressive in three starts after missing the beginning of the season with a torn tendon in a finger on his pitching hand.
Iwakuma hasn't allowed a run in his last two starts, surrendering eight hits without issuing a walk in 16 innings. In last Tuesday's 2-1 loss to Tampa Bay, he was set to win a fifth straight start dating to last season before the bullpen gave the game away in the ninth.
Still, he hasn't been charged with a loss since Aug. 10, an 11-start streak in which he's 6-0 with a 1.61 ERA. Two of those outings came against the Rangers, and he went 2-1 with a 2.94 ERA in five matchups last season.
"He's better than I thought," Mariners first-year manager Lloyd McClendon told the team's official website. "I knew sitting in the other dugout that he was good. He's better than good."
Colby Lewis (3-2, 4.99) hasn't fit that description in six starts back from elbow and hip surgeries, though his last outing was his best as he struck out eight over 5 2-3 innings in last Monday's 4-0 win in Houston. He'll now try for consecutive victories while making it through six innings for the first time this season.
"I'm trying to go as deep as I can in ballgames," said Lewis, who threw a season-high 108 pitches. "Sometimes it doesn't work out because I get my pitch count up. One of these days I'll get there. I'm not too concerned about it."
Two of his starts have come against Seattle, in which he's 0-1 with a 6.10 ERA.
The Mariners will try to again get to Lewis after Sunday's 6-2 victory in Minnesota ended a four-game losing streak. Robinson Cano went 4 for 5, upping his average to .318 with a 7-for-14 series, and he's reached base in 26 straight games.
Lewis' former Texas teammate Justin Smoak is 6 for 11 with a home run and two doubles against him, while Corey Hart is hitless in 10 at-bats with five strikeouts.
Hart left Sunday's game with a strained left hamstring and was scheduled to have an MRI on Monday.
"It didn't look good," McClendon said. "We'll know more tomorrow after the MRI. From that, we'll decide what we're going to do."
Adrian Beltre 8 for 22 with two home runs against Iwakuma, but Moreland and Leonys Martin are a combined 3 for 30.