A Cubs source said Wednesday that Mateo was upset with the club's decision to send him to Single-A ball. The source added that Mateo left the Tennessee club en route to Mesa, Ariz., site of the Cubs' minor league offices, rather than Daytona.
"He purposefully skipped his plane," the source said.
If Mateo files necessary paperwork consenting to retirement, he could be placed on the Cubs' voluntary retired list, or the restricted list. No less than six months could pass before Mateo could request to be reinstated by the club, should he desire.
Mateo made his big league debut with the Cubs in 2006, making 10 starts and finishing 1-3 with a 5.32 ERA in 45 2/3 innings. He was an All-Star at Double-A West Tennessee that year, going 7-4 with a 2.82 ERA in 17 starts.
A season ago, the right-hander began the year on the disabled list with a strained right shoulder and did not make his 2007 debut until June. He would go on to log 62 1/3 innings, most of which were with Iowa.
RHP Esmailin Caridad started Wednesday in place of Mateo.