Kyle Busch Motorsports released Jason Leffler on Tuesday after a disappointing season so far in the team's No. 18 truck.
Leffler had just one top-five finish in nine starts for KBM this season, which team owner Kyle Busch said was not up "to the standards we've become accustomed to."
"We owe it to our manufacturer and our sponsors to produce better results," Busch said in a statement. "Beginning to make these changes now, instead of waiting until the end of the season, it will allow us to evaluate where our program stands as we begin working towards becoming a championship-contending team once again in 2013."
Kurt Busch will drive the No. 18 truck this weekend at Michigan, but a replacement for Leffler's races will be named at a later date. Leffler was originally scheduled to drive 14 races for KBM this year.
Brian Scott will drive the truck in four more races – including Bristol – and Drew Herring will make his series debut in the No. 18 at Iowa.