"I thought I did something really bad to it," Floyd said. "But it's just a strain. No tears. I'm day to day."
Asked if he'll be ready for the opener, Floyd said, "Hope so."
Despite the receiver's optimism, he will have the results of his MRI sent to other specialists, including Dr. James Andrews, to confirm the initial diagnosis, league sources told ESPN NFL Insider Ed Werder.
Even if the initial diagnosis is accurate, it is expected that the earliest Floyd would be able to return would be the regular-season opener against the Texans in the second half of ESPN's "Monday Night Football" doubleheader and possibly not until Week 2 when the Chargers travel to play the Eagles.
The reason Floyd is seeking a second opinion is that small tears in ligaments are often difficult to see. Floyd will not personally visit Andrews unless the doctor makes that determination after reviewing the scans.
The preliminary results of an MRI performed Monday night prompted the team to report Floyd has a knee strain, which suggests damage to muscle or tendons rather than ligaments stabilizing the joint.
A team source texted Monday night regarding the MRI results, saying "good news" without elaborating further.
Floyd sustained the injury in a collision with cornerback Shareece Wright during practice Monday. The team's other starter at wide receiver, Danario Alexander, was lost for the season after he tore the ACL in his right knee in a collision with Wright last Tuesday.
A source said there is no current time frame on when the team's leading receiver will return.
Floyd has been solid during his Chargers career but also has been slowed by injuries. He has played in 16 games only once, in 2009. He missed two games with an ankle injury last year but still led the Chargers with a career-high 56 catches, for 814 yards and five touchdowns.
After Floyd got hurt, Eddie Royal and Vincent Brown were working with the first team. Royal was slowed by injuries last year, his first with San Diego, and Brown missed all of 2012 after breaking his left ankle in a preseason game.
ESPN's Shelley Smith and Ed Werder contributed to thsi report. Information from The Associated Press also was used.