The 31-year-old winger has been in impressive form for Besiktas this season, combining with the likes of Ryan Babel, Ricardo Quaresma and Cyle Larin - though he has been in and out of Senol Gunes' side.
The ex-Sunderland star shone against Sarpsborg under Leeds' watchful eye, scoring twice as Besiktas came from 2-0 down to secure a sensational 3-2 win and give themselves a huge chance of qualifying for the knockout stages.
It is believed that scouts were impressed with the Holland international's display against Sarpsborg, and are now expected to make a bid for the attacker with the January transfer window fast approaching.
Lens played for Sunderland during the 2015-16 season, scoring four goals and creating three more in their Premier League campaign. But he was shipped out on loan the next season, as Sunderland were relegated during 2016-17.
Now, a sensational return to England could be on the cards for Lens with Leeds looking to sign the attacker in the January transfer window. The ball remains in Besiktas' court, though, with his contract expiring in the summer of 2022.
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