CHICAGO — It was supposed to be his fourth start of the 2023 season, but that will have to wait for one of the Cubs’ newest starting pitchers.

Before the beginning of a four-game series with the Dodgers on Thursday, the Cubs put Jameson Taillon on the 15-day injured list with a left groin strain that’s been described as “mild to moderate.”

Manager David Ross said on Thursday that it happened while playing catch before the series finale against the Athletics in Oakland on Wednesday.

He was scheduled to take the mound for the Cubs at Wrigley Field on Thursday, with Michael Grove opposing him for Los Angeles. Instead, Javier Assad will pitch for the Cubs after he was called up from Triple-A Iowa on Thursday in what will be his first start of the season.

Assad was on the Cubs’ Opening Day roster, pitching out of the bullpen in two games before being sent down on April 10.

Signed as a free agent after spending the last two seasons with the Yankees, Taillon has pitched in three games so far with the Cubs, sporting an 0-2 record with a 4.50 ERA with 16 strikeouts compared to four walks.

His first two starts were at Wrigley Field, giving up three runs and seven hits in four innings during a loss to the Brewers on April 2, then five runs and six hits to the Rangers in a loss on April 9.

Taillon had a much-improved outing against the Dodgers last Saturday, pitching five shutout innings with seven strikeouts compared to two walks over the course of 85 pitches.

Drew Smyly will take the mound for the Cubs on Friday against the Dodgers with Hayden Wesneski getting the ball Saturday and Marcus Stroman pitching in the finale on Sunday.