Brock Purdy, 49ers’ top receivers ruled out for Thursday night at Rams

SANTA CLARA — Brock Purdy and his troublesome toe are returning to the 49ers’ bench.

Mac Jones will start at quarterback as Purdy is sidelined for the third time in four games Thursday night when the 49ers (3-1) visit the Los Angeles Rams (3-1).

Purdy will have company on the SoFi Stadium sideline: wide receivers Ricky Pearsall (knee), Jauan Jennings (ribs, ankle) and Jordan Watkins (calf) also got ruled out Wednesday.

Jones will wear a left-knee brace after aggravating a posterior cruciate ligament sprain in the home-opeing win against Arizona. Jones also started the Week 2 win at New Orelans. Purdy returned for Sunday’s 26-21 loss to Jacksonville. Purdy said Tuesday that he wouldn’t be able to play if the 49ers were playing that night but left open hope he could push the decision until game day.

Pearsall was off to a tremendous start to his second season, with a team-high 327 receiving yards on 20 catches with no interceptions. But Pearsall sustained a posterior cruciate ligament injury and felt instability to pull himself from last Sunday’s game.

So who will Jones target without the 49ers’ would-be starters in Pearsall and Jennings? Demarcus Robinson, formerly of the Rams, figures to enter the starting lineup along with Kendrick Bourne, who had three drops in Sunday’s loss to the Jaguars.

Skyy Moore and Marquez Valdes-Scantling also should be in uniform, and the 49ers could promote Russell Gage Jr., Malik Turner or Junior Bergen from the practice squad.

Jones’ backup will be Adrian Martinez, who’s already been elevated from the practice squad twice; players can only come up three times in a season without joining the 53-man roster.

The 49ers also could promote a defensive end, Trevis Gipson or William Bradley-King, to help cover for Robert Beal Jr., who’s been ruled out with an ankle injury. Listed defensive tackle C.J. West (thumb) as questionable, but cleared to play are cornerback Renardo Green (neck) and defensive lineman Mykel Williams.

The Rams’ listed two players as doubtful: tight end Tyler Higbee (hip) and right tackle Rob Havenstein (ankle).