Joe Greenspan started and played only his second match as a Loon on Tuesday. The center back came back from a concussion endured in his first match, the June 14 U.S. Open Cup contest, to be the lone available center back for United in a 1-0 loss to Columbus.

Francisco Calvo and Jermaine Taylor are on national team duty, while Brent Kallman and Vadim Demidov are injured, along with four other Loons.

This was Greenspan's second concussion this year, as he had one at the start of the season that kept him out for several weeks until he went on loan to the United Soccer League's Pittsburgh Riverhounds.

"It's been frustrating because with a lot of injuries, you have a bit of a layoff, but you can start rehabbing and doing things to rehab the muscles or the ligaments, get them stronger so that when you come back, you're in good shape, and you're ready to go," Greenspan said, adding he hadn't really had any concussions before this stint.