Colts running back Marlon Mack did not play in the second half of Sunday’s 27-20 loss to the Jacksonville Jaguars due to an ankle injury and Indianapolis fears that the running back tore his Achilles, a source told ESPN’s Adam Schefter.

Coach Frank Reich said Mack will have additional tests on the injury Monday.

Mack suffered the injury after catching an underneath pass in the second quarter. He immediately grabbed his ankle, got up and took off his helmet before waving for assistance from the Colts’ sideline. The Colts brought a cart to the sideline and had it transport Mack to the locker room. He left the game with four rushes for 26 yards and three catches for 30 yards.

Mack, who rushed for a career-high 1,091 yards in 2019, missed at least two games in each of his first three seasons with the Colts. The team did not offer Mack a contract extension during the offseason.

Depth at running back is not a problem for the Colts. Nyheim Hines, who had two touchdowns in the first half, and rookie Jonathan Taylor became the primary running backs after Mack left the game. The Colts also have Jordan Wilkins in the backfield.