Bertrand moved to Villa Park until the end of the season midway through the January transfer window, starting all three of the side's games since then and earning the plaudits of his manager.
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"He's a terrific guy and I'm delighted with him. It's just a loan the way it stands but you'd never think the boy was only on loan the way he's settled in and the way he's played.
"Ryan's earned the right to have a value, whatever that may be, because of what he's done.
"Whatever Chelsea price him at, that's their prerogative but we're thankful they gave us that opportunity to let him come here."
The signing of Bertrand has created greater competition for places at Villa, with the likes of Antonio Luna dropping down the pecking order, and Lambert insists that being left out of the team is something all players have to come to terms with.
"It happened to Ron Vlaar last year, Karim El Ahmadi as well," he added.
"It was hard for them to come into a new environment, and they had played at Feyenoord in front of big crowds every time.
"It is difficult and you're fortunate if they can hit the ground running. Some players can do it from the off and others tend to take a bit of time."