"When there's something that's involved with your neck, we want to check it out really good," Cubs manager Lou Piniella said. "It's nothing serious, and we think he'll be here [Tuesday]. He's day to day, depending on how he is when he shows up [Tuesday]."
Lee, who is the National League's leading hitter with a .390 average, was taken to Chicago mainly because it was easier for the Cubs to arrange the tests than to try to do something in New York.
With Lee out of the lineup, Mark DeRosa started at first base in Monday's game against the Mets, and Alfonso Soriano moved from leadoff to third in the order for the first time this season. The switch is temporary.
"When Derrek comes back, we'll put D-Lee back in the three hole," Piniella said.
DeRosa has started three games at first base in his career.
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.