As if beginning the season 0-2-0 wasn't difficult enough, the Union were dealt another blow late Tuesday night, when right back Sheanon Williams got word that he'd received a call-up for national duty.

Williams (pictured, left, with Freddy Adu) will fly to Nashville Wednesday morning to join the U.S. U-23s, who christen their Olympic qualifying tournament Thursday with a 9 p.m. match against Cuba. Union teammates Freddy Adu, the U-23 captain, and Amobi Okugo are already in Nashville.

A defender, Williams inked what he told reporters is a five-year contract extension this offseason. In doing so, the Union locked up a rising talent on the national circuit ... which makes the notion of losing Williams for as many as the next two games a concern.

Williams, who had been in the U-23 camp this offseason, along with Adu and Okugo, will miss Saturday's match at Chicago and stand to miss the March 31 date against visiting Vancouver, assuming the U-23s advance to the CONCACAF semifinal and beyond.

Following Thursday's match with Cuba, the U.S. U-23s take on Canada Saturday, then El Salvador the following Monday, March 26. The semifinal and final matches are March 31 and April 2.

Already a weak link for the Union, the backline would suffer a serious hit if Williams was to miss the next two matches. The Union have relinquished five goals in two matches, both defeats, to open their season. No team in Major League Soccer has surrendered as many.

And with Danny Califf's status unknown -- at least until Wednesday, when Union manager Peter Nowak addresses the media -- the backline has a serious hole.

(Times staff photo / JULIA WILKINSON)