Shelvey, who played with N'gog at Anfield before the latter joined Bolton in 2011, has claimed that the Frenchman will show his best form at the Liberty Stadium.
"I worked with him for 18 months at Liverpool so I know what he can do," Football365.com quotes Shelvey as saying.
"David had a good record at Liverpool. But, with no disrespect to him, there were a lot of far bigger names in front of him at Anfield like Fernando Torres.
"He couldn't get too much of a look-in. But if he gets a chance here, he'll take those chances. At this club, the fans make you feel loved."
N'Gog could make his Swansea debut against West Ham United on Saturday.