Virgil van Dijk's superb form for Liverpool could become a problem for Jurgen Klopp if the Reds do not win the Premier League title this season, according to Garth Crooks.
Van Dijk has been one of the standout players in Liverpool's title charge this season, with the Netherlands international leading by example in a defence which has conceded just 15 goals in 29 League games.
Liverpool's goalless Merseyside derby draw at Everton on Sunday meant Manchester City held on to top spot in the table with nine games left, though Klopp's side sit just a point behind the champions.
Van Dijk is increasingly being talked about as a potential PFA Player of the Year winner, with the world's most expensive defender justifying his £75million transfer fee following a January 2018 move from Southampton.
The Dutch centre-back earned further plaudits for an assured display in Sunday's Merseyside derby, though former Tottenham forward Crooks believes it is exactly those sort of performances which will have Clasico rivals Real Madrid and Barcelona considering summer transfer bids - especially if Liverpool fail to win the title.
"Virgil van Dijk: What a colossus this man is," Crooks told BBC Sport.
"In the white-hot heat of a Merseyside derby, Virgil van Dijk was simply immense.
"Whatever needed to be done was completed with composure and style.
"On a day when Liverpool's strikers looked more like the three stooges than the red arrows, Van Dijk took it upon himself to try and score the goals as well as defend his own penalty area.
"The problem for Liverpool is simply this; if they don't win the title this season the chances are Real Madrid or Barcelona will come knocking - probably both. And few turn them down."
Liverpool have lost two key players to Barcelona in recent years, with Luis Suarez moving to Camp Nou in 2014 before Philippe Coutinho followed in a deal potentially worth £142million in January 2018.
Barca have already agreed a £65m deal for 19-year-old Dutch defender Matthis de Ligt to join them from Ajax this summer, while Real could be in the market for a defender depending on their managerial situation this summer after falling well behind Barca in the Spanish title race.
