Williams missed Swansea’s 1-0 friendly win over Rennes on Saturday, along with Wales team-mate Neil Taylor and Iceland’s Gylfi Sigurdsson.
“I don’t know the future,” said Guidolin.
“But I can say that right now Ashley Williams is our player, he is training with us.”
Swansea begin their Premier League campaign at newly-promoted Burnley on Saturday, 13 August.
With Williams, Taylor and Sigurdsson missing all of the Swans’ pre-season friendlies, Guidolin has yet to decide how many – if any – of the Euro 2016 trio will feature at Turf Moor.
“He [Williams] is a little bit later than others but it is normal for him,” the Italian added.
“I don’t know about playing next week. It is difficult because he has only just begun to work in the last days.”
Although Williams was missing against Rennes, there was a first start for new signing Fernando Llorente after the Spain striker joined from Sevilla on Friday.
But the World Cup winning forward did not start his Swansea career the way he would have wanted as he missed a glorious opportunity in the first half, squandering an open goal by hitting the post from close range.
Swansea dominated the match and eventually won it thanks to a header from Jay Fulton, who had only been on the pitch a matter of seconds having come on as a substitute.
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