Lengthy injury history
One of the biggest concerns for signing Dalvin Cook is that he not only has nearly 1,300 rushing attempts in his career, but he has also battled a number of injuries during that time. He has played a full regular season slate of games once, which was last year, and has missed at least two games every season prior to that.
In his rookie season, Cook suffered a torn ACL after only four games and missed the remainder of the season. Then in his second season, he suffered a hamstring injury that forced him to miss four games.
In addition to that, he has dealt with a shoulder injury over the past three seasons that could have impacted his performance on the field. According to Tom Pelissero, he did get surgery this offseason to correct that injury but when considering adding an older running back, durability has to be a concern.