The 26-year-old was forced to wait patiently for his chance at Pride Park, only making his Derby debut in January, five years after he joined the club from Nuneaton Town.
But Roos has seized his chance with both hands, keeping five clean sheets in 13 games while often keeping the veteran Scott Carson out of the starting XI.
With the Dutchman out of contract in the summer, Frank Lampard could be about to lose one of his players on a free.
Second tier rivals Stoke, Hull and Bristol City are all circling, hoping to snap up one of the league’s more underrated shot-stoppers without spending a penny.
Stoke potentially see Roos as a replacement for the England international Jack Butland.
The Sun reported earlier this year that Crystal Palace are planning a £15 million for Butland, whose international prospects won’t be helped by a second successive season of Championship football.
Roos could be a solid, if cheap, successor.
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