On Saturday Tommy Bowe marked his return to action with a double, and Ulster romped to a 47-17 victory, scoring seven tries in all.
Zebre managed two of their own, through Guglielmo Palazzani and Ulrich Beyers, but Guidi wants the team to be more aggressive although he admits it will be tough to end their winless run before the end of the campaign.
He said: "We found ourselves under pressure too often; especially in one-on-ones. That's not good for a team like Zebre which has to make aggression a distinct characteristic.
"The game is a warning bell which we have to pay attention to. The responsibility is on all of us: there's no question this run of defeats doesn't help our confidence even if honestly, if we keep playing like this it will be hard to go and win at Glasgow and against Newport, who are playing the Challenge Cup semi-final.
"We'll need to show a different attitude and application. Injuries are no excuse: now there is a chance for everybody and all the players have to take advantage of it.
"We can't have two faces this season: the really positive one of the start of the season, and this one."
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