Wales coach Warren Gatland said Jenkins, who was man of the match, would have a scan on Monday for what appeared to be an anterior cruciate ligament (ACL) tear.
The flanker suffered the injury when he was cleared out of a ruck and his leg got stuck. He received treatment on the pitch for several minutes after the final whistle with several players from both sides going over to check on him.
Depending on the severity of the injury, Jenkins could struggle to be fit for the start of the World Cup in Japan next September.
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"It looks like an ACL which is not brilliant. He’s very disappointed," said Gatland.
"When you see a player who has worked hard to win his spot and get in the team, pick up an injury, you feel for him."
The 25-year-old Cardiff Blues captain had been a late inclusion in the side after the elbow injury suffered by Dan Lydiate on the eve of the test.
The victory saw Wales complete a clean sweep of their November test series for the first time and extended their winning run in test rugby to nine games.
(Reporting by Mark Gleeson, editing Peter Rutherford)
