The 49ers once had the best linebacking duo in the NFL when All-Pros Patrick Willis and NaVorro Bowman were making tackles all over the field.

But ever since Patrick Willis retired in 2015 and Bowman sustained his career altering knee injury in the 2013 playoffs, things haven’t been the same. To compound things, Bowman is rehabbing from an Achilles tear suffered Week 4 that puts his start of next season in jeopardy.

It’s no surprise the 49ers’ once-elite defense is now dead last in both scoring and yardage in Chip Kelly’s first season as coach. Improving the middle of the defense will be a mandate this spring.

Bleacher Report’s NFL draft guru Matt Miller posted his latest mock draft this week, projecting San Francisco to fortify its defense with the best inside linebacker available with the second-overall pick: Alabama’s Reuben Foster.

Foster recently won the 2016 Butkus Award given to the nation’s top linebacker for his work in Nick Saban’s vaunted defense.

Foster would be a great addition to the heart of San Francisco’s defense that badly needs an upgrade at inside linebacker. Michael Wilhoite and Nick Bellore haven’t played well replacing Bowman and Ray-Ray Armstrong, while Gerald Hodges has struggled to seize an every-down role.

ESPN’s draft expert Mel Kiper wrote about Foster this week:

He could be the best of the stellar group of Crimson Tide inside linebackers to be picked in the first round recently (Rolando McClain, Dont’a Hightower and C.J. Mosley). Foster is a complete player. Top five isn’t out of the question, which is rare for an ILB. He’s that good.

Related Uninspiring QB class creates questions for 49ers atop NFL draft

Foster looks like a slam-dunk pick for San Francisco, but they also did well in the second round of the mock. Miller’s projection had the 49ers landing Clemson’s Deshaun Watson, considered by many the top quarterback available.

Watson’s athleticism and skill set would fit well within Kelly’s offense if Kelly is back for a second season. But there are questions about Watson’s ability to read defenses and throw accurately, which is why his draft stock dipped this season.

But Watson takes on Ohio State in the College Football Playoff and could enhance his standing with a good performance against arguably the best secondary in the country.

There’s no question the 49ers need to improve the middle of their defense and find a quarterback early in the draft. Taking Foster second overall and landing Watson round two look like great decisions for San Francisco.