The Buffalo Bills pulled a thrilling comeback against the Baltimore Ravens in their season opener last Sunday to clinch a narrow 41-40 win. While Josh Allen & Co. are heading into the Week 2 game against the New York Jets under their belt, former NFL head coach Rex Ryan had a potential warning for the Bills.Ahead of the Bills' game against the Jets, Rex Ryan called out Buffalo's sluggish running game against the Ravens as a potential weak link. Ryan feels the Jets could upset the Bills by taking advantage of their running game,"The Bills can't hide from what we saw last week. They couldn't stop the run."The Bills recorded 238 rushing yards allowed in Week 1 against the Ravens, the 32nd best in the league. In comparison, the Jets rank fourth in rushing yards with 182 yards on the ground against the Pittsburgh Steelers in their season opener.If the Jets' offense ran like they did against the Steelers, they could find much joy against the Bills, who are without Defensive tackle Ed Oliver for the Week 2 clash, causing an upset.Justin Fields holds the key for Jets' upset against Josh Allen-led BillsWhile Josh Allen will be a key figure for the Bills after his heroics in the season opener, the Jets will be relying on quarterback Justin Fields after his solid debut for New York against the Steelers.Fields had an excellent debut for the Jets, making 16 of his 22 passes for 218 yards and a touchdown, along with two rushing touchdowns. It was reminiscent of his performance in the Steelers' season opener last year.The Jets saw the potential of the 26-year-old quarterback, signing him to a two-year, $40 million contract in March. He was announced as the starting quarterback for the team by general manager Darren Mougey later that month.