I can't think of any version of Grundy that has a chance here. Yes, Sinestro could easily fling him into space, but you said no BFR. Still though, Sinestro can fly and has ranged attacks, plus forcefields and all that other nonsense. Grundy is essentially a slow moving brick. The most powerful versions of Grundy can be quite durable, but the problem is he can't fly and has no ranged attacks and Sinestro can just pelt him with energy attacks from afar at his leisure.
It's certainly possible Grundy is capable of doing some super leaps like The Hulk, but Sinestro could still just fly out of the way.
IMO most powerful Grundy has ever been was in a classic tale vs Alan Scot, Classic Fate and Hourman. Grundy's power comes from the fact that his body absorbs energy to give him his strength and durability, its why his levels fluctuate. He's always more powerful around more powerful adversaries who use their energy on him. In the story in question he'd been in a swamp that radioactive waste had been dumped, and as such had absorbed so much energy (from attacks of Fate and Allan plus radioactivity) that aside from being stronger he developed powerful TK to the point he was tk throwing half a town (wood) at Allan and tk threw Fate and hourman at each other
That version wins, sinstros attacks would only make him more powerful