Cashner hurled a scoreless inning of relief in Tuesday's 6-5 loss to the Twins.
Cashner (11-7) pitched four scoreless innings of relief, allowing only two walks while striking out three in Friday's 7-6 win over the Angels.
Cashner will pitch out of the bullpen moving forward, Chris Cotillo of MassLive.com reports.
Cashner's spot in the rotation is safe while David Price (wrist) is on the injured list, but he may be removed as the Red Sox consider the rotation moving forward, Chris Cotillo of MassLive.com reports.
Cashner surrendered three runs on three hits and five walks while striking out one over 1.2 innings Sunday against the Angels. He didn't factor into the decision.
Cashner (10-7) allowed six earned runs on seven hits and two walks while striking out four across 5.1 innings to take the loss Tuesday against the Royals.
Cashner (10-8) took the loss Thursday, surrendering seven runs on seven hits and five walks while striking out one over 5.2 innings to the Rays.
Cashner (9-5) allowed four runs on six hits with two walks and seven strikeouts across six innings while taking a loss against the Orioles on Sunday.
Cashner was traded from the Orioles to the Red Sox on Saturday in exchange for 17-year-old prospects Elio Prado and Noelberth Romero.
Mikolas (9-3) won his third straight decision by pitching seven innings Saturday against the Blue Jays, allowing just one run on three hits with four strikeouts and no walks.