CHICAGO -- A day after Rich Hill sprained his left knee during a start against the Cubs, the Red Sox placed the 42-year-old lefty on the 15-day injured list prior to Saturday’s game.

Hill joins Nathan Eovaldi (low back inflammation) and Garrett Whitlock (right hip inflammation) on the injured list at a time Boston’s rotation depth is getting tested.

In 15 starts this season, Hill is 4-4 with a 4.20 ERA. The lefty feels that this injury is similar to the MCL sprain he suffered with the Dodgers at the beginning of the 2019 season that forced him to miss a month.

Nick Pivetta and Michael Wacha -- who are both All-Star candidates -- are the only members of the team’s rotation from the start of the season to remain on the active roster.

The good news is that ace Chris Sale, who hasn’t pitched this season due to a stress fracture in his right ribcage, could return as soon as July 11.

Eovaldi threw a 35-pitch bullpen session Saturday at Fenway Park, marking the second time he’s been off the mound this week.

Whitlock is also making strong progress but he will be used as a reliever when he is activated, Red Sox manager Alex Cora confirmed on Saturday.

The Red Sox don’t have an off-day until the All-Star break starting July 18, so they will continue to entrust Triple-A prospects with opportunities.

Josh Winckowski, the club’s No. 13 prospect according to MLB Pipeline, started Saturday’s game against the Cubs. It was Winckowski's fourth start of the season and third since Whitlock and Eovaldi went down.

No. 14 prospect Connor Seabold is likely to be recalled from Triple-A to start Sunday’s series finale against the Cubs. Seabold gave up seven hits and three homers in 4 2/3 innings to the Blue Jays earlier this week, but showed some promise by generating 21 swings and misses in his second career start.

Wacha and Pivetta will open the upcoming homestand with starts on Monday and Tuesday against the Rays.

It is unclear if the Red Sox will call up another starter for Wednesday or go with a bullpen game.

Could Brayan Bello, the club’s No. 4 prospect, be called on to take that turn in the rotation?

Bello threw 5 1/3 innings for Triple-A Worcester on July 1, and Wednesday would be his normal day to pitch. The righty is the best pitching prospect the Red Sox have had in years.

“There’s a lot of guys in the mix for a lot of stuff here now,” said Cora. “All of a sudden, there’s a lot of stuff health-wise that is going on. We’ve been talking about those guys the whole season. Let’s see what happens in the upcoming days.”