Baker signed a one-year, $5.5 million contract with Chicago in the offseason. The right-hander's last major-league start came on Aug. 8, 2011, and he underwent Tommy John surgery in April of 2012.
Cubs president Theo Epstein originally hoped that Baker would be ready in mid-April, telling Carrie Muskat of MLB.com in November:
"He's put the work in to get himself on an excellent timetable so he's got pretty much every day plotted out from here through Spring Training. If things go perfectly, he'll be stretched out to five or six innings for that first week of the season."
Baker suffered a strained muscle in his pitching elbow during his first spring training start on March 17, which caused him to miss most of the season. Baker made eight rehab starts in the low-minors before joining the Cubs.
The starter spent part of seven seasons with the Minnesota Twins, going 63-48 with a 4.15 ERA. Baker had been enjoying a strong 2011 campaign, posting a 3.14 ERA over 134 2/3 innings before being shut down.