Gates and Mathews both sat out practice again on Friday and Chargers coach Norv Turner was less than optimistic when asked about Mathews' status for Monday night.
"I doubt a guy can improve enough in two days to be healthy enough to play on a Monday night," Turner told The San Diego Union-Tribune. "... If he improves dramatically I would consider playing him."
Gates, suffering from a torn plantar fascia in his right foot, is likely to miss his second straight game after sitting out Sunday against Houston.
Mathews, a first-round pick in April, has been beset by injuries in his first year in the NFL. The Fresno State product re-aggravated a right ankle sprain in Week 10 and missed the second half against the Texans. If Mathews doesn't play Sunday, it would be the second time he was inactive this season.
If Mathews is unable to go, the Chargers would likely start Mike Tolbert for the third time this season.
The Union-Tribune also reported that wide receiver Malcom Floyd suffered a slight setback Friday in his return from a hamstring injury that has sidelined him since Week 6. However, Turner said he's hopeful Floyd will be able to return on Monday.
"We do have a little bit of time to get him some rest and hopefully he'll be all right," Turner told The Union-Tribune.
Fellow wideout Legedu Naanee practiced on a limited basis Friday as he aims to return from his own hamstring ailment. Also, Kicker Nate Kaeding has practiced fully the past two days after missing the last three games with a groin injury.