It looks like they miss WR Sidney Rice, and he can't come back fast enough.
But in case Rice doesn't come back, or comes back at less than 100%, the Vikings have found Plan B. According to Pro Football Talk, they've become the "primary suitor" for unsigned WR Vincent Jackson. He's probably about the most similar player to Rice (both are tall WRs who are more known for their size then their speed) and he's legit because he's been one of the best WRs in the NFL over the past two seasons.
Jackson's no easy trade target. The Chargers probably want value in return (unlike the Steelers who dumped WR Santonio Holmes for a low draft pick) and Jackson wants a big contract. Plus he's got a substance abuse suspension looming. He'll be suspended for three or six games, depending on how next week's hearing turns out, and obviously he's got some sort of problem with a banned substance. Maybe it's a big deal, but maybe it's not.
Since Jackson is certain to miss time over the first few weeks, the Vikings interest (if it's real) might not be about looking for a receiver to replace Rice while he's out. Rice is supposed to return after the first six weeks of the season and Jackson might not be available for six weeks either. But maybe the Vikings are concerned that Rice might not return to full health at all this season.