CHICAGO – The unknown is almost more difficult than the physical pain Cubs third baseman Ian Stewart deals with every day.

Stewart has battled a sore left wrist for almost a year – the same wrist that ended his season with the Colorado Rockies last August – undergoing several tests that were inconclusive. Despite trying to battle through the pain, Stewart landed on the 15-day disabled list Thursday. The Cubs purchased the contract of Triple-A Iowa infielder Luis Valbuena, who started at third base in the series finale against the Tigers.

Stewart, acquired in an offseason trade, is hitting .201 with five home runs and 17 RBIs in 55 games. He admitted to frustration at a lack of diagnosis, especially because he can feel something in the wrist causing the soreness.