San Francisco 49ers sign new quarterback hours before Rams showdown with Brock Purdy injured

San Francisco 49ers have promoted quarterback Adrian Martinez from their practice squad following Brock Purdy's latest injury setback. 

The 49ers face the Los Angeles Rams at SoFi Stadium on Thursday night and, hours before kick-off, reports confirmed they had added Martinez to their 53-man roster.

It's understood that Martinez will serve as the 49ers' backup QB for Mac Jones, who is set to start the Week 5 fixture.

Ian Rapoport revealed that the 49ers have also elevated DE Trevis Gipson and WR Malik Turner from the practice squad ahead of the game. 

Martinez had not made an appearance in a regular season game.

First-choice QB, Purdy, meanwhile, missed Weeks 2-3 with a toe injury suffered against the Seahawks - but was able to return for their game last weekend.

However, after defeat to the Jaguars, Purdy reported further discomfort in his toe.

GM John Lynch subsequently came out and said the 49ers will take 'every precaution to make sure Brock's all right' - before he was later ruled out of the game.

Purdy has been pegged as the team's quarterback of the future, which is why he was given a five-year contract extension in May. 

The lucrative deal is worth $265 million, with $181 million in guaranteed money, quite the investment from San Francisco. 

Head coach Kyle Shanahan knows getting the proper return on that contract is key to his job, with him not throwing Purdy into harm's way being a smart move. 

Former NFL quarterback Steve Young discussed Purdy's ongoing injury problems, on 'Pardon the Interruption', ahead of their game on Thursday night. 

He said: 'It's the ligament in the big toe. He's a righty so it's on his right foot and that's the plant foot… The whole throw is through your right big toe if you think about it. 

'So for Brock, you saw him last week, he had to stay off of it. So what you do is you start your throwing motion, and you can't dig in with your toe, so you come over the top like a catapult, so all of a sudden your throws are high and not as crisp. So you have to manage.' 

Jones, meanwhile, had a fast start to his career, helping New England make the playoffs in his rookie season. But Jones regressed the next year after offensive coordinator Josh McDaniels left for Las Vegas, and he was replaced as the starter.

Jones was traded to Jacksonville last March and started seven games for the Jaguars, throwing eight touchdown passes and eight interceptions. 

So far this season, when filling in for Purdy, Jones has made two appearances, completed 53 of his attempted 80 passes and thrown four touchdowns.