Published: 2019-08-16 00:28:13 BdST
Barca's all-time top scorer and captain Messi injured his calf in training before his side's brief pre-season tour of the United States and has not yet returned to full training a day before his side visit Athletic.
Videos emerged on Thursday of the Argentine getting up to speed in individual training sessions on sand but Valverde said there was no chance he would gamble with Messi's fitness.
"We never like to risk any players and much less someone like Leo," Valverde told a news conference on Thursday.
"He still hasn't returned to training with the team and while we are happy with his progress, individual training is very different to playing a match. We are going to wait and see."
Barca have spent over 200 million euros on signings including Frenkie de Jong and Antoine Griezmann but continue to be linked with a second swoop for Neymar, two years after he left the Catalans for PSG for a world record 222 million euros ($246 million).
Valverde refused to answer questions about the club's interest in Neymar and lamented the fact that the Spanish transfer window does not shut before the season starts, as it does in England.
"It's inconvenient and it's not logical. The normal thing would be that the team you start with is the same one that will compete for the whole season," Valverde said.
"Now we have two weeks until the transfer window shuts and you can't breathe easily until then. I'm very happy with the squad I have at the moment but I don't know what will happen next.
"I am far removed from transfers and I'm focusing on the players I have for our first game," he added.
"Neymar belongs to PSG and we'll see what happens but I can't say anything more about him."
Barca's game in Bilbao was only confirmed last Friday after a court case was settled between the league's organising body and the Spanish football federation over scheduling games outside of the weekend.
Valverde criticised the two bodies for their handling of the situation.
"It seems incredible to me that the war over the match days and schedules was not solved before hand, the image of the league and federation has been damaged as a result," he added. ($1 = 0.9011 euros)