The Red Sox will be without All-Star first baseman Willson Contreras as they look to complete a series sweep of the Chicago White Sox Thursday night.

Contreras did not return for the top of the fifth inning of Wednesday night’s eventual 4-0 series-clinching victory, due illness the club later announced. Anthony Seigler entered at second base, while utility-man Nick Sogard moved over to replace Contreras at first.

“He’s good, he’s a little under the weather,” Red Sox interim manager Chad Tracy told reporters postgame of Contreras. “Just feeling a little sick and took some temperatures as the game was going on, the temperature started to go up and he started to get a little dizzy so we felt like it was best to get him out of there.”

Tracy said the Red Sox were not concerned about a link between illness and the head injury Contreras suffered on a hit-by-pitch in Friday’s series opener at the Los Angeles Dodgers. He missed Saturday’s game while under concussion protocols, but returned to the lineup Sunday.

“No, no, he was just feeling ill and we gave it a while,” Tracy said, “and got to the point where he was starting to get dizzy so we felt it wasn’t conducive to keep going.”

Contreras certainly appeared to be playing up to the impressive standard he has set for himself in his first All-Star season since 2022: a .288/.395/.540 line, 104 hits, 18 doubles, a team-leading 23 home runs, 57 runs and 70 RBI in 105 games. Before he exited the game, he went 1 for 1, his go-ahead RBI single in the bottom of the first giving the Red Sox a lead they would ultimately hold until the end. Contreras also impressed defensively in the top of the third, throwing from first to home in time for catcher Connor Wong to apply the inning-ending tag on White Sox outfielder Sam Antonacci.

The National Weather Service issued a Heat Advisory for most of southern New England Thursday through Saturday, as the heat indices across the region may reach up to 100 degrees, and cautioned the public that the high temperatures and humidity may cause “heat illnesses.” It was 89 degrees at Fenway when the Red Sox announced Thursday’s lineup.

Red Sox lineup

Nick Sogard 1B

Ceddanne Rafaela CF

Wilyer Abreu RF

Caleb Durbin 3B

Masataka Yoshida DH

Andruw Monasterio SS

Jarren Duran LF

Anthony Seigler 2B

Connor Wong C

Ranger Suarez P