"It's frustrating," Willis said. "I worked real hard to get back and finally get in a groove and this happens. I'll overcome it. I've done it before. Just go back to the drawing board."
Willis was selected in the eighth round in 2000, but the Cubs dealt him to the Marlins in March 2002 -- a six-player deal in which Chicago got Antonio Alfonseca. Willis won 14 games and the National League Rookie of the Year Award in 2003. Now 31, Willis also has played for the Marlins, Tigers, Diamondbacks and Reds. He last pitched in the big leagues in 2011.
Willis was an extra on the Cubs' travel roster and the seventh pitcher in Monday's game. The Cubs needed extra arms after starter Carlos Villanueva failed to finish the first, reaching his pitch count after five batters.
Willis ended up being the pitcher of record and took the loss, as Evans scored to lead the Dodgers to a 7-6 win. The lefty will be re-evaluated on Tuesday at Fitch Park. He said he's had this fatigue problem before.
"I've just got to do a better job doing the maintenance of keeping my shoulder and arm strength up," Willis said, sitting in a corner of the visitors' clubhouse at Camelback Ranch. "It's not so much the lifting and stuff, but doing things to keep my shoulder strong. It's just frustrating because I finally get a chance and hit the ground running. If guys can overcome ACL tears, I'll overcome this and come back.
"I'm just frustrated today. I really wanted to play and mix it up. It's early, so hopefully I have enough time to come back."
His plan now is to "work smarter, not harder." Willis isn't ready to give up.
"You keep fighting, keep competing," he said. "I'm sure it's nothing serious, I'm sure it's just fatigue and stuff like that. God willing, I'll spend a couple days of getting that stuff worked out and get right back on the field. I don't want to miss a lot of significant time."