Guruzeta was speaking to Onda Cero Bilbao ahead of Saturday's Basque derby against Deportivo Alavés at Mendizorroza — the 500th game of Valverde's reign and one of the most loaded fixtures of the season for both clubs.
"It's a shame he's leaving. For me he's a legend, the best coach we have had and that the club has had. With him we have had four very, very good years, apart from this one which is slipping away from us a little. I hope we finish well with him, for him, for us and for the fans."
Valverde announced before the season that this campaign would be his last in charge at San Mamés. Athletic have had an inconsistent year, weighed down by injuries and a demanding Champions League campaign that stretched the squad beyond its limits.
Guruzeta, who has matched his personal best of 16 goals for a season this term, acknowledged the difficulty of a year in which individual returns have felt hollow without the collective rewards to match.
"It's been a year with many blows we weren't expecting, many injuries, many defeats. Last year we managed to make ourselves strong at home and this year it hasn't been like that."
He was also candid about the emotional toll of scoring without winning.
"I consider myself a team player, even though I'm a striker and I'm scoring. I don't like losing. The feeling we've had all year of taking that step to win and getting up there and not managing it — when you score and you don't win, you go home miserable."
Athletic sit three points outside the European places with five games remaining. Guruzeta has not given up on the dream of finishing Valverde's tenure with continental football secured.
"If we end up getting into Europe, it's a very beautiful way to say goodbye to Ernesto. Most years he has qualified for Europe. The numbers he's done with Athletic show it and it's going to be very difficult to take that word legend away from him as a coach. Europe is very close."
Saturday's derby at Mendizorroza brings its own tension. Alavés are fighting for survival, Athletic for a European spot, and the stakes ensure neither side will concede ground easily.
"It's going to be a tough game, a derby in which we both have a lot to play for. Away from home has been costing us quite a bit, so hopefully on Saturday we can turn the situation around."
On the growing speculation linking former Borussia Dortmund coach Edin Terzić with the San Mamés dugout, Guruzeta was typically direct.
"We have enough on our plate. I've taken myself off social media and every day I find out less. When the manager who comes is made official, we'll know then."