Is it okay for a bunch of players to fight one high level monster? (D&D 4th Edition)?

In my campaign I'm designing, I have about five or six players with an NPC companion face off against a level seven Troll. I did the math, and assuming they follow the general plot they will be around level 3 characters. Is it a good idea for them to fight something so powerful, even if it is only one monster? I mean, a level 7 creature that has no super overpowered abilities shouldn't be too much of a problem. From my knowledge of the game, I don't see very many problems with it, and I can never get the encounter formula exactly right; usually it is too easy or too hard for the players, so I would like to get some outside opinions on this one. Thanks for your advice!