Later in the day, the Red Sox obtained left fielder Tommy Pham in a trade with Cincinnati for a player to be named or cash.
The 35-year-old Diekman is 5-1 with a 4.23 ERA in 44 appearances this season. The 6-foot-4 reliever is particularly tough on left-handed hitters, holding them to a .188 batting average this year.
“I know he can be very nasty,” manager Tony La Russa said after the White Sox lost 2-1 to Kansas City on Monday night to drop back to .500 at 51-51. “So he’ll help us.”
The Red Sox also traded catcher Christian Vazquez to Houston for minor league infielder Enmanuel Valdez and outfielder Wilyer Abreu.
The Red Sox and Astros played in Houston on Monday night, so Vazquez had a short trip to join his new team. Vazquez, who turns 32 on Aug. 21, hit .282 with eight homers and 42 RBIs in 84 games with Boston this year.
The White Sox are trying to make it back to the playoffs for the third straight season after winning the AL Central in 2021.
Diekman’s contract calls for $3.5 million salaries this year and next, and it includes a $4 million team option for 2024 with a $1 million buyout.
The 27-year-old McGuire batted .225 with 10 RBIs in 53 games with Chicago. He was acquired in a trade with Toronto in April.
“Reese has been a really great teammate and he’s going to a good position in Boston,” La Russa said.
McGuire became expendable for the White Sox when Yasmani Grandal returned after being sidelined by lower back spasms. McGuire also was outplayed by catcher Seby Zavala, who was batting .296 with two homers in 30 games heading into Monday night’s series opener against Kansas City.
The Red Sox are well off the pace in the loaded AL East, but they still have a chance for a wild card.
Pham was hitting .238 with 11 homers and 39 RBIs in 91 games this season for the Reds. The 34-year-old ranks third among left fielders with seven outfield assists.
A nine-year veteran, Pham is a career .261 hitter with 108 homers and 339 RBIs. He spent his first 4+ big league seasons with the Cardinals and has also played for the Rays and Padres.
Pham made headlines in May when he was suspended for three games by Major League Baseball after he slapped San Francisco Giants outfielder Joc Pederson because of a dispute about their fantasy football league. While the Giants warmed up in the outfield before the series opener with the Reds, Pham confronted Pederson and smacked him in the face before they were separated.
Pham gets a $500,000 assignment bonus for being traded. He has a $6 million salary this year as part of a deal that includes a $12 million mutual option for 2023 with a $1.5 million buyout.
Valdez, 23, hit .296 with 10 homers and 32 RBIs in 38 games for Triple-A Sugar Land this season. The 23-year-old Abreu batted .249 with 15 homers, 54 RBIs and 23 steals in 89 games for Double-A Corpus Christi.