A joint investigation is underway at Mount Diablo High School in Concord after its new football field was damaged in fire over the weekend, just days before the season opener.

The cause of the fire is still under investigation, according to the Contra Costa County Fire Protection District.

Lt. Kevin Halm with the Concord Police Department said the suspect(s) have not yet been identified.

Both firefighters and officers responded to the fire at the high school's field on Sunday morning, but new findings indicate the fire could've sparked much sooner. It took firefighters about five minutes to extinguish the flames.

"Initially, the investigation was concerned with 'Was an accelerant or something poured on the field?' Now, reviewing surveillance footage, it looks like fireworks were being set off on Saturday night, so the night prior. That likely caused a fire that smoldered until the morning hours. But we don't want to rule out the possibility that there was something else that happened, but more than likely, that's what occurred," Halm said.

Arson investigators also took samples of the field.

The field cost somewhere between $1 million to $3 million to install, according to Liz Mangelsdorf, the school's vice principal. It's unclear how much it'll cost to repair.

"We've been investing a lot of money into the program, both the football team and the girls flag football team. And so, we've been working to really build up all the sports teams here. So, having this state-of-the-art field was a big boost for our kids," Mangelsdorf told CBS News  Bay Area. "It was going to be flagship field of Mt. Diablo Unified School District. And because of whatever the cause was, it's really devastating - especially to the football players."

Coming off of their most successful season in decades, Mt. Diablo High School Football will defend its first league title since 1962.

This Friday's game which was both the team's season opener and home opener, will now be played at Concord High School. It's unclear where the rest of the team's home games will be played, as officials are still assessing the best options, according to Mangelsdorf.

The recovery of the field is also dependent on the turf itself.

"The most time it's going to take is to get the turf shipped here. It's a specialized turf. It's not local," Mangelsdorf said. "The turf has to be shipped here, then they have to get the installers. I think once that happens, they can do it fairly quickly."

Mangelsdorf is hoping the football team can play at least half of the season on their new home field, but added "there's really no way to tell."