Aaron Ramsey has been ruled out of Wales' opening Euro 2020 qualifier against Slovakia through injury.
The 28-year-old was withdrawn late on in Arsenal's 3-0 Europa League triumph over Rennes prior to the international break.
Juventus-bound Ramsey has been struggling with a thigh problem and did not feature in the friendly win over Trinidad and Tobago at Wrexham's Racecourse ground on Wednesday night.
He was also absent from Wales' training session at Cardiff City Stadium on Saturday morning.
And it has been confirmed that Ramsey - who has since returned to Arsenal - will miss the game against Slovakia.
"Aaron's gone back to Arsenal. He won't be available tomorrow," said Giggs.
"His injury didn't clear up in time so it's obviously a blow. Especially with the form that he's been on and with the quality that he's got. He's not made it but that gives someone else a chance.
"He gave it a try yesterday and it just wasn't settling down as quickly as we thought but it was just too short a turnaround really.
"We made sure that we had a plan B and we've been working on that during the week. We had two options. Of course you're going to miss someone like Aaron but we prepared for if he didn't make it aswell."
Speaking about Ramsey's absence, Gareth Bale said: "Obviously it's a big blow for us, he's a big player for us and we'll obviously miss him.
"But it gives someone else a chance to step in, do a good job and hopefully help the team to get a win."
Euro 2016 heroes Wayne Hennessey, Ben Davies, Joe Allen and Bale are all expected to start against Slovakia having been rested for the 1-0 triumph over Trinidad and Tobago in midweek.
But due to Ramsey's absence, Giggs will have to draft in an additional attacker to his side.
The likes of David Brooks and Harry Wilson are expected to start, but others including Swansea City's Daniel James, Leeds United's Tyler Roberts and Liverpool youngster Ben Woodburn will all be pushing for a place in the XI as a result of Ramsey's absence.
Possible Wales XIs: Hennessey; C Roberts, A Williams, Mepham, Davies; Allen, Smith; Brooks, Wilson, James; Bale / Hennessey; C Roberts, A Williams, Mepham, Davies; Allen, Smith; Brooks, Bale, Wilson; T Roberts.
