Minnesota United center-back Brent Kallman has been suspended 10 games and fined 20 percent of his $136,456 annual salary by Major League Soccer for violating the league's substance abuse and behavioral health policy, the club announced on Thursday.

United stated that Kallman tested positive for an unnamed performance-enhancing substance.

The 28-year-old will miss Minnesota's four remaining regular-season matches of 2019 -- at Portland, against Sporting Kansas City and LAFC, and at Seattle -- plus any playoff games the club participates in this season, and any remaining matches in the 2020 regular season. Kallman may not participate in training or use team facilities to train during his suspension, with the exception of preseason ahead of 2020.

The St. Paul-based Pioneer Press reported on Thursday that Kallman consumed an undisclosed substance as he recovered from an upper-leg injury over the summer.

"That's when I gave in and I caved to the pressure and I started taking something," the Pioneer Press quotes him as saying. "Now I'm paying the consequences for it."

Kallman has made 16 appearances in 2019, serving as the Loons' third center-back, behind Ike Opara and Michael Boxall. Prior to 2019, the Twin Cities native had made 47 appearances in the two seasons since United moved up to MLS from the NASL.