"Nick's been a very accurate kicker in this league for a long time," coach Anthony Lynn said Thursday. "He's been here before. We're familiar with him, and he has experience in big games. As you know, every game we've played has been a close game, and every point matters."
The Chargers have started the season 0-4, losing three of those games by three points or fewer.
Koo had a potential game-tying kick blocked in the final second of a 24-21 Week 1 loss to the Denver Broncos and then missed what would have been a game-winner in the final seconds of the Chargers' 19-17 Week 2 loss to the Miami Dolphins.
Overall he was 3-for-6 on field goal attempts this season while converting all nine of his extra-point attempts.
This will be the 36-year-old Novak's second stint with the Chargers. He previously kicked for the Chargers from 2011 to 2014. He made 101 of his 117 field goal attempts with the Chargers and 156 of his 157 extra-point attempts.
He was with the Houston Texans the past two seasons but was released by the team before the start of this season.
In 10 NFL seasons, Novak has converted 82.8 percent of his field goal attempts (173-for-209). He is 239-for-245 on extra-point attempts.
"I take a lot of pride in wearing the lightning bolt and the name on the back of the jersey," Novak said. "Like I said, I just want to be a good teammate. It's great to play; it's not so fun being out there watching."
Novak said he'd been training at his home nearby in San Diego when he got a call from the Chargers on Wednesday. Novak said he also attended the Chargers' last home game against the Philadelphia Eagles last week to check out his potential new surroundings at the StubHub Center.
"Koo's a very talented kicker," Novak said. "He's got a live leg and a lot of talent. I actually went to the game last week with my wife and watched him in warm-ups, watched him throughout the game and I was really impressed with his leg strength."
The change at kicker comes after Lynn vowed to make changes following the Chargers' winless start.
Lynn had this to say when asked why he didn't make the change at kicker two weeks ago.
"Two weeks ago, Koo was kicking the ball fine," Lynn said. "He had the one bad outing against Miami, but players have a bad day, a bad game every once in a while. But watching him over the last couple weeks in pregame and practice, I've seen enough. It was time to bring in someone with a little more consistency, a little more experience.
"But I think Koo is going to have a long NFL career. I told him that this happens to a lot of rookies. A lot of rookies get cut early in their career, and they come back and play for a lot of years. And he may be back here, who knows?"