rihanna (with iv)

*The arm with the IV that you see above belongs to Rihanna.

Sources close to Rihanna say she came down with a bad case of the flu and required an IV drip.

Sources tell TMZ she started feeling really ill last week and saw a doctor on Thursday, but by the time of her “Saturday Night Live” appearance, she still wasn’t fully recovered.

As we first reported, Rihanna missed the SNL dress rehearsal because she was sick — but show producers didn’t buy her excuse … insisting she didn’t appear ill.

But looks might be deceiving — because we’re told Rihanna wasn’t just ill during her SNL performance, she also continued to feel sick the next few days … and her doc was forced to put her on penicillin.

Soon after, Rihanna began to experience flu-like symptoms — requiring IV treatment yesterday, which is when she posted the above picture on Twitter.

We’re told she’s feeling much better now.

In other RiRi news, her camp says she’s NOT dating Raiders running back Darren McFadden despite reports the two were spotted together in Hawaii a couple weeks ago.

Sources close to Rihanna tell us, the singer did meet Darren last month in Honolulu — while she was promoting her new film “Battleship” — but they kept things strictly platonic.

We’re told Darren — who was WITH HIS GIRLFRIEND — introduced himself to Rihanna as a fan … and Rihanna bought Darren and his GF drinks on the beach. That’s it.

But that doesn’t mean Rihanna can’t support her new pal — which might explain why the singer wore a Raiders jersey to a New York strip club last week.