Paul Lejjena, a staff sergeant with the US Army's 1st Battalion, 41st Infantry Division, is in a serious condition with broken limbs, burns and internal injuries, according to a report on Wednesday on a website run by California-based Marshall Islander Aenet Rowa.
Lejjena's unit was on patrol in Baghdad last Thursday when a roadside bomb exploded nearby.
More than 100 Marshall Islanders are estimated to be serving in the US Army, with about 20 of them in Iraq or Afghanistan.
Citizens of the Marshall Islands, Palau and Micronesia are eligible to join the US military under a Compact of Free Association that closely links the island nations with Washington.
In exchange for hundreds of millions of dollars in funding, Washington has defence control of this central Pacific region, which covers an area the size of the continental United States.