According to ProFootballTalk.com, Jonas Jennings could return to the team soon after their game against the Baltimore Ravens.

A league source tells us that the San Francisco 49ers could see the return of tackle Jonas Jennings as soon as this week following a leave of absence for personal reasons.

Per the source, the team gave Jennings a week off as a result of multiple personal issues that came together all at once.

One of the issues, as we understand it, is an illness to a member of his immediate family. We don't have specific information as to any of the other problems he's experiencing, but we're told that there's no issue with Jennings himself.

The 49ers are on a bye for Week Six, and return to action on October 21 when the travel to the Meadowlands to face the Giants.

Source: http://www.profootballtalk.com/rumormill.htm