Troubled Quins sit bottom of the Guinness Premiership table after three consecutive defeats and they now face being without Jordan Turner-Hall, who requires surgery on his shoulder, until the new year.
"We can't underestimate the quality that Harlequins have got, despite the fact that they are yet to win a game this season," said Bates. "Despite their injuries they still have an excellent squad to pick from, and they have quality right throughout their back row which is capable of hurting any team."
He added: "They've got an exciting back line with an excellent kicker in Nick Evans, and we know we will have to be very efficient if we are going to put them under some pressure during the game.
"Quins will naturally be disappointed at the way in which they've started the season, but they could quite easily turn that around with the quality they have in their squad."