The San Francisco 49ers are currently going through an injury crisis. This is led by injuries to tight end George Kittle and 49ers quarterback Brock Purdy. Both of these players have been key to the teams recent success, but will now spend time on the sidelines.On Friday's edition of 'The Herd", NFL analyst Colin Cowherd believes that this team will struggle with one player singled out as a key reason for these issues."Mac Jones will be the starter."Mac Jones is the former quarterback for the New England Patriots and played his college football under Nick Saban at Alabama. However, as we have seen with many former Crimson Tide QBs, success in college does not translate into success in the NFL.Jones started his time in the league strong with a rookie season where he was able to throw over 3000 yards and even take the Patriots to a playoff spot. However, Jones has never been able to repeat this success and has progressively declined in form since that season.Under him, the Patriots stuggled (losing their status as one of the best teams in the league) with Jones being a key reason. After the Pats traded him to the Jags, he again led his new team to a poor season. His time with Jacksonville only lasted one season, and he is now the backup at the 49ers.But now, due to Purdy's injury, Jones has been given the reins of the team. If his prior form is anything to go by, the team will want Purdy back as soon as possible if they want to avoid a very disappointing season.How long will Mac Jones be the 49ers QB?49ers fans may have to get used to Mac Jones as their quarterback, as on Thursday, an update was given on the injury to Brock Purdy. According to 49ers GM John Lynch:"What we're dealing with is kind of a week-to-week thing. That's our information. Brock's doing well, coming back from it. We'll just treat it as such. He's doing a nice job, doing everything he can to get back out there as soon as possible. That's where we're at."It was later confirmed that Purdy will be out for 2-5 weeks.Best case scenario for 49ers fans is that Purdy makes a quick return a takes over from a Mac Jones that has been able to lead the team to a win in what will be difficult circumstances due to the injuries.The worst case is that Purdy is out long term, and Jones massively struggles, leading to a returning Purdy playing what would essentially be meaningless games.