The Swans midfielder has enjoyed a terrific campaign in Wales this season after leaving north London last summer.
And Keown sees him as one of the Premier League's best players full stop - not just in his own position.
As such, the former Arsenal defender finds it very difficult to believes Spurs sold the 'quality' 25-year-old to Swansea. Tottenham have relied on the likes of Christian Eriksen and Nacer Chadli for their goals and assists this term - but Erik Lamela, Andros Townsend and co have underwhelmed.
The BBC Pundit told Match of the Day: “Sigurdsson is, for me, one of the best players in the division. He does so much for Swansea and is such a quality player.
“He has goals, assists and he’s very quick footed and an intelligent player. Really, I can’t believe Tottenham let him go.”
As Opta stats show, just two Spurs midfielders/wingers have scored more goals this season than the Swansea man.
In terms of assists, however, no one within Mauricio Pochettino's squad really comes near the Icelandic international.
And, considering Tottenham's struggles out wide and down the middle at times this season - as well as their lack of depth in terms of quality - you can certainly see Keown's point.
Swansea won't mind, however...