Clemons will undergo an MRI on Monday to confirm the injury.
Seattle's best pass-rusher, Clemons hurt his left knee in the third quarter of Sunday's game and did not return.
"We're concerned about it," Seahawks coach Pete Carroll said after his team's 24-14 comeback win.
Losing Clemons, 31, would be a significant blow to a Seattle defense that ranked No. 1 during the season with 15.3 points allowed per game.
The ninth-year veteran had 11.5 sacks during the regular season, tied for ninth-most in the league. Clemons also had 40 total tackles, three forced fumbles and a fumble recovery.
Seattle, the fifth seed in the NFC, visits the top-seeded Atlanta Falcons in the divisional round next Sunday.
Information from ESPN NFL Insider Adam Schefter and The Associated Press was used in this report.