The Vikings signed Harnish to the practice squad after rookie quarterback Teddy Bridgewater suffered an ankle injury in last Sunday's win over the Atlanta Falcons. He was promoted to the active roster before Thursday night's 42-10 loss to the Green Bay Packers.
With Bridgewater unavailable, Christian Ponder started for the Vikings, completing 22 of his 44 pass attempts for zero touchdowns and two interceptions.
After the game, coach Mike Zimmer said Bridgewater would return for next week's game against the Detroit Lions. Bridgewater took over the Vikings' starting job after veteran Matt Cassel suffered a season-ending foot injury in a Week 3 loss to the New Orleans Saints.
Over three games with Minnesota last season, Line, who went undrafted out of SMU in 2013, caught one pass for eight yards.