Michael Waltrip Racing revealed on Tuesday that it has switched the crew chiefs and engineers for its No. 15 and No. 55 teams in the Sprint Cup Series.

Effective immediately, Brian Pattie will become the crew chief for Ragan's No. 55 Toyota. Ragan is substituting for Brian Vickers in that car for the remainder of this season since Vickers is presently taking blood-thinning medication for blood clots, which prevents him from being able to race.

Billy Scott will take over crew chief duties for the No. 15 Toyota, driven by Clint Bowyer.

Additional changes at MWR include a reorganization of lead, secondary and support engineers for each team. Car chiefs, road mechanics and pit crews will remain with their originally assigned teams.

Pattie has been Bowyer's crew chief since the No. 15 team at MWR was established in 2012. He has scored three wins with the team and finished second in the '12 Chase for the Sprint Cup championships as well as seventh in the 2013 Chase.

Scott has been the crew chief for the No. 55 since August 2013. He previously served under crew chief Rodney Childers as that team's lead engineer.

Bowyer is currently 17th in the point standings, with just three top-10 finishes for the season. Ragan is ranked 23rd in points.

Sprint Cup is competing at Michigan International Speedway this weekend.