Crystal Palace sent a personal representative of club chairman Steve Parish to Lille to watch transfer target Ibrahim Amadou in action against Strasbourg, according to Sky sources.
Amadou, 24, put in a man-of-the-match performance in central midfield as Lille beat Strasbourg 2-1 at the Stade Pierre-Mauroy.
Crystal Palace had an improved bid in excess of £16m for Ibrahim Amadou turned down by Lille earlier this week.
The Eagles had a £16m bid for the Cameroon defender turned down earlier in January, according to Sky sources, and also held talks with Lille a year ago for the 24-year-old.
Palace have tried to sign Amadou on loan but Lille prefer a permanent move.
Sky Sports News understands Amadou is valued at about £20m but Lille’s financial problems mean they would sell for less.
The Ligue 1 side need to raise €25m to avoid potential relegation to Ligue 2 for breaking French financial fair play rules.