Chicago Cubs pitcher Carlos Zambrano will undergo an MRI scan on Monday in Chicago on his right elbow after having to leave Saturday's game early because of tightness. "He was going back [to Chicago] for the off-day anyway," Cubs athletic trainer Mark O'Neal said Sunday about Zambrano. "While he's home, basically for precautionary reasons, we'll send him back and get it checked out so we know exactly what we're dealing with." Zambrano was pulled after 3 1/3 innings on Saturday, and O'Neal described the problem as similar to tennis elbow. He took the loss, a 4-3 decision to the Nationals, and is 3-2 with a 4.09 ERA. "The complaints today are the same that they were last night, not any worse," O'Neal said. "We're talking 10 to 12 hours from when he was pitching in the game, so for it not to be worse, in my mind, is a good sign." Zambrano, 23, said he felt fine until Washington's Vinny Castilla hit a two-run single off him in the fourth inning. Zambrano faced three more batters after that before exiting. "It's nothing to worry about," Zambrano said. "It's not a cramp, but a tired arm, fatigue. I will try to do the best possible to be on my schedule and not miss any starts."