Van Persie faces former club Arsenal tomorrow.
"When a ready-made, world-class player comes into the team it gives everybody a lift," Giggs told ManUtd.com and PA Sport.
"We're like the supporters - we look forward to playing with and seeing quality players come into the team. Robin is certainly that - he's proven that with his goals and all-round play since he's come to the club.
"Robin's set-piece delivery has been really important to us. It's a big plus this season that we're scoring from set-pieces and corners. That's something we haven't done over the last few years as often as we'd have liked.
"So with Robin it's not just goals you get. He's helped add more goals to the scoresheet and helped a few different names get on there."