The Red Sox have made a switch in the bullpen ahead of this week’s series in Houston, calling up right-hander Greg Weissert while optioning left-hander Bailey Horn to Triple-A Worcester.

Weissert was one of the club’s most reliable bullpen arms through the first half but was among those whose production fell off dramatically in July. Weissert posted a 2.65 ERA as of June 25, but over his last 11 MLB appearances between June 28 and July 28 he allowed an 8.53 ERA, raising his total for the season to 4.24.

Since going to the minors he’s appeared in four Triple-A games, and in those outings he’s allowed one earned run over six innings (1.50 ERA).

Horn has appeared in 14 big league games for the Red Sox this season, posting a 6.48 ERA in 16.2 innings. He appeared in three of Boston’s four games against the Orioles this past weekend.

The Red Sox will hand the ball to Tanner Houck (8-8, 3.01) to start Monday’s opener, and he’ll face off against Houston left-hander Yusei Kikuchi (6-9, 4.49). Boston’s lineup will lean heavily right-handed, with Tyler O’Neill, Rob Refsnyder, Romy Gonzalez, Danny Jansen, Connor Wong and Ceddanne Rafaela all set to start while Masataka Yoshida and Wilyer Abreu come off the bench.

Jarren Duran CF

Tyler O’Neill RF

Rob Refsnyder LF

Rafael Devers 3B

Romy Gonzalez 2B

Danny Jansen C

Triston Casas 1B

Connor Wong DH

Ceddanne Rafaela SS

When: 8:10 p.m.

Where: Minute Maid Park, Houston, Texas

Broadcast info: NESN, WEEI 93.7 FM, WCCM 1490 AM (Spanish)