Chelsea reportedly watched teenage forward Alexander Isak in action for Willem II earlier this month.
Isak was linked with a number of clubs before joining Borussia Dortmund from AIK in January 2017.
The forward only scored once in 13 appearances for Dortmund, though, before joining Dutch outfit Willem II on loan in the January transfer window.
The 19-year-old has struck 11 times in 11 Eredivisie appearances in the second half of the 2018-19 campaign, and it has been reported that Barcelona are considering a summer swoop.
According to The Mirror, though, Chelsea watched the forward score for Willem II against Ajax earlier this month and the Blues are now tracking the four-time Sweden international's progress.
The Premier League side are currently waiting to learn whether they have won their appeal against a two-window transfer ban imposed by FIFA.
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