Dallas (ankle) didn't take part in Wednesday's practice, John Boyle of the Seahawks' official site reports.
Dallas sat out Weeks 14 and 15 due to a high-ankle issue, but he's been able to play in both of the last two games, racking up a cumulative nine carries for 53 yards and nine catches (on 10 targets) for 87 yards. His absence to kick off Week 18 prep may be a precaution in order to avoid a setback leading up to the regular-season finale, but with Kenneth Walker (ankle/illness) and Travis Homer (ankle) also sitting out Wednesday, the Seahawks' backfield situation again is up in the air ahead of Sunday's contest against the Rams.