It is "tough but possible" for Premiership sides to compete both domestically and in Europe, says Northampton Saints director of rugby Phil Dowson.

Dowson's side have endured a difficult defence of their Premiership title but are the only English club remaining in this year's Investec Champions Cup quarter-finals after Harlequins, Saracens, Leicester Tigers and Sale Sharks were knocked out in the last 16.

Saints, who are seeking to become the Premiership's first Champions Cup winners since Exeter in 2020, can reach a second consecutive semi-final in Europe's premier club competition if they overcome Castres at Franklin's Gardens on Saturday.

The Premiership salary cap increased to 6.4m this season but it is still considerably lower than the 9m cap for Top 14 clubs in France, and after last weekend's dire showing by English clubs in general, former England and Lions wing Ugo Monye suggested they found it "hard to compete" as a result.

But Dowson, who guided his side to the Premiership title and a first Champions Cup semi-final since 2011 last season, told BBC Radio Northampton: "It is hard [to compete] but it's supposed to be hard.

"Some of the other sides and leagues have more ability to withstand injuries and rest players but it's still possible for Premiership teams.

"The Top 14 has a longer schedule and they may have bigger squads but they still have to ensure they are winning every week to compete on two fronts, likewise in the United Rugby Championship.

"It is possible but it's tough. We haven't managed to do it very well this year but last year we had a decent run in the tournament and it's a very tough thing to do."