The Dutchman has received strong praise from the former Newcastle boss.
The 25-year-old has shone since arriving at St James' Park over the summer, scoring against Liverpool as the Magpies earned a rare Premier League win on Sunday afternoon - and also claiming another effort some thought was an own goal from Martin Skrtel.
And Keegan is quoted as telling beIN Sport by the Chronicle: "Wijnaldum could be the best signing the owner has made.
"He was fantastic. Newcastle had a bit of luck (with the first goal) but when you’re down the bottom you don’t normally get that kind of luck.
"It normally goes the other way. It’s good to see the players smiling again."
It's very early in Wijnaldum's St James' Park career, of course, but that does make his immediate impact even more significant.
If the Dutchman can achieve this much (he has netted seven Premier League goals already) this soon, the rest of the season could be very promising indeed for Wijnaldum.
The 25-year-old will need to deliver once again at White Hart Lane on Sunday afternoon, as Newcastle travel to Tottenham Hotspur for another typically tough top-flight clash.
Holding strong at the back and hitting Spurs on the break could be an effective strategy - but it is unlikely even Liverpool would produce as lethargic a display as they did on Sunday if given a second chance.