The number of baseball players born outside the United States and featured on Major League Baseball opening day rosters this week slipped to its lowest level in four years, the league said on Tuesday.

As MLB's 30 teams begin their 2010 season this week, 27.7 percent of players, or 231 of the 833 listed on opening day rosters, were born outside the US, the league said.

That is down from last season when 28 percent of players, or 229 players of the 818, were born outside the US. It also marks the lowest level since 2006 when 27.4 percent of 813 players were foreign-born.