Neil Lennon says he saw similarities between Virgil van Dijk and ex-Manchester United defender Rio Ferdinand when he arrived at Celtic in 2013.
Van Dijk joined the Hoops from Groningen in a £3 million deal seven years ago, and went on to feature in 113 matches in all competitions for the club.
The Netherlands international impressed enough at Celtic to earn a £12m ($15m) move to Southampton in 2015, where he spent two-and-a-half seasons before being snapped up by Liverpool.
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The Reds lured the 28-year-old to Anfield for a then world-record fee for a defender of £75m ($94m), and he has since established himself as arguably the finest centre-back in European football.