Watson crocked as Quins edge it
Bath 19-25 Harlequins
England suffered an injury scare just three weeks before the Six Nations when Anthony Watson limped out of Bath's 25-19 Heineken Champions Cup defeat against Harlequins.
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Watson, one of England's star performers at the World Cup in Japan, went off nursing a leg problem 11 minutes into the second-half.
The Bath full-back underlined his frustration in front of watching England head coach Eddie Jones by hurling his gum-shield to the ground before leaving the action.
England look like being without injured Exeter centre Henry Slade for the early Six Nations action, with the World Cup runners-up facing France in a Paris opener on February 2.
Bath, meanwhile, are staring at a first top-flight European whitewash after Quins won the Pool Three encounter thanks to tries from flanker James Chisholm, wing Gabriel Ibitoye and number eight Alex Dombrandt, while Brett Herron kicked two conversions and two penalties.
Bath managed three touchdowns of their own - hooker Jack Walker, wing Gabe Hamer-Webb and centre Jackson Willison the scorers - and Freddie Burns added two conversions.
The west country club have never lost all their pool games in a European campaign.
But a 16th season of European Cup rugby will officially be their worst if they are toppled by Ulster next Saturday and suffer a sixth successive defeat in the series.
Bath and Quins had already been eliminated from the quarter-final race, trailing way off a scorching pace set by Ulster and French heavyweights Clermont Auvergne who meet in France today.
And Quins emerged victorious at the Recreation Ground, guaranteeing that Bath will finish bottom of the group and confirming a miserable European campaign.