Beckham, 26, said the quad had been bothering him for a few days. The team's training staff finally decided enough was enough and he needed to give it time to heal. Beckham missed close to two months with a broken bone in his wrist earlier this season, but otherwise he's been pretty durable in his five-year career.
In 66 games coming into Thursday, Beckham was hitting a solid .308/.360/.418 (109 OPS+) with three home runs and five stolen bases. His defense also rates as above-average, hence 1.6 WAR in a little more than one-third of the season. Prior to 2013, Beckham had an 84 OPS+ and 4.7 WAR in 535 career games.
The ChiSox have the second worst record in baseball at the moment (46-74), which is why they sold off veteran players at the trade deadline. Beckham was one of the team's few bright spots in an otherwise miserable campaign.
Chicago selected Beckham with the eighth overall pick in the 2008 draft.