Giggs was Louis Van Gaal’s assistant at Old Trafford when Rashford broke through at United in sensational style.
Rashford, then 18, scored twice on his first-team debut in a Europa League draw in February 2016, and the Manchester-born forward has become a regular starter for club and country .
“Marcus is a talent,” Giggs said ahead of their Wembley reunion on Thursday. “Having worked with him, I saw what a fantastic mentality he has.
“He’s a player who wants to improve and be the best. He realizes that he will have to improve like all young players.
“He’s one of the many English players that we will have to look for in their attacking line if they play. ”
Rashford took time to regain his form after the lockdown following return surgery in January.
But the 22-year-old recovered to his best at the start of the new season, opening his Premier League account with a brilliant solo goal in United’s 3-2 win at Brighton last weekend.
“Obviously as a United fan it was awesome,” Giggs said.
“When a player like that scores a goal like that, it doesn’t matter who it is, it’s great and what the fans want to see.
“If he’s in that kind of shape, you’ve got some work to do to try and stop him.
“We know we will have to be at our best and on our toes to stop Marcus and the other England players. “
Wales do not have captain Gareth Bale, who has remained at Tottenham to get back in shape after his loan transfer from Real Madrid.
Bale suffered a knee injury on international duty last month, but Giggs will be hopeful Aaron Ramsey will come in Sunday’s Juventus game for the midfielder to start a Wales game for the second time in close to two years.
Former captain Ashley Williams, now 36 and without a club after leaving Bristol City at the end of last season, has not been included in the 27-man squad.
“The door is still open for Ash,” Giggs said. “It doesn’t matter how old a player is, whether young or old.
“If they’re playing well and they still want to play for Wales, which Ash is doing, then there’s no reason to close the door. “