Lindegaard, who had been without a club since leaving Preston in the summer, joined the Clarets on a free transfer after the dislocated shoulder suffered by Tom Heaton last month.
The former Manchester United man has made two appearances for Duff's Under-23 side in the Professional Development League, helping the Clarets to clean sheets away at Hull City and then in the 1-0 win over Leeds at Curzon Ashton on Monday night.
"He showed his quality in the last five minutes when the ball was coming into the box. His kicking was excellent," Duff told the Lancashire Evening Telegraph of Lindegaard.
"Considering he's been out for a while, I think it was his second game in (11 months), but you could see his quality at the end, coming for crosses and diffusing the situation when we were under the cosh.
"He showed what he's all about."