It's a mistake that they don't have a vet WR in here. There's no reason to not give Will Fuller a call and bring him to camp. He won't cost much so if he doesn't work out, the cap implications aren't all that great. You simply can't rely on Tolbert and Brown to be good enough to not have teams completely double Lamb all game long.
People are in love with Tolbert but he's a third round rookie who likely is going to need time to find his legs. Look at Gallup. It wasn't until mid to late in his rookie year that he started to show what he has. And even then, he only had 33 catches as a rookie. Expecting Tolbert, for example, to be some viable #2 is a risk at this point.