The mild discomfort Edwin Jackson felt in his lat muscle in his right arm didn't seem as serious as his desire to rebound from a historically lousy season.

"I started off shaky and ended shaky" Jackson said Saturday after suffering his 18th loss in a 6-2 defeat to the Cardinals. "I know my potential and what I'm capable of doing. That's what I look forward to. Three more years and going out like I know I can pitch."

The Cubs didn't expect Jackson 30 to post the most losses since Bill Bonham lost 22 in 1974 or possess a 4.98 ERA in the first season of a four-year $52 million contract.

Jackson was pulled after 22/3 innings after allowing six runs and feeling tightness that started in the bullpen. Neither manager Dale Sveum nor Jackson believed the injury was serious but correcting his problems for 2014 seemed more urgent.

Jackson downplayed any speculation that he was putting too much pressure on himself to pitch well with a new contract for a new team.

"There might have been times I was overanalyzing and thinking too much and not allowing myself to go out and do what I'm capable of doing" Jackson said.