DENVER, Colo. (TNND) — During Sunday’s NFL game, the Los Angeles Chargers did not have their head coach Jim Harbaugh right before kickoff against the Denver Broncos.

Just minutes before kickoff at Empower Field in Colorado, Harbaugh entered the blue medical tent with trainers. It was unclear why he was checked out and what was going on. Minutes later, Harbaugh was seen walking back to the locker room and ultimately missed the start of the game.

The Chargers brought in defensive coordinator Jesse Minter as interim head coach. The team confirmed that Harbaugh was dealing with an illness and they were unsure whether or not Harbaugh would return to the game.

Halfway through the first quarter, Harbaugh returned to the field and took over for Minter. It is still unknown what his illness was.

This is Harbaugh’s first season as Charger’s head coach after nine years at Michigan. Last year, he ended his tenure at Michigan with a national championship.

The Chargers are currently 2-2 going into Sunday’s game.