When Garde arrived at Villa back in November, he believed that the forward lacked the physical qualities to play in the Premier League.
However, Kozak has been working hard in the gym - and he was rewarded with a start against Crystal Palace last night.
The Czech Republic international put in an excellent display, and helped Villa pick up their first win in 19 Premier League matches.
And Garde said: “I was pleased with Libor. I think he worked very hard for the team.
“He could have scored - but I think he was finally offside on a good throughball.
“When I arrived at the club, I thought he needed to work more physically. It was not easy for him.
“I saw in the last two weeks that he was in better shape. His training sessions were better.
“I thought he could be the one today to help us to win. I knew he had a tough time. But he never let down his attitude. He is very professional.
“He showed me he could be very helpful for the team.”
There had been suggestions that Kozak could leave Villa in January, with Birmingham City one of the clubs said to be interested in signing the striker by the Birmingham Mail.
Kozak’s recent resurgence should keep him at Villa Park though, and he will be hoping to prove his worth.
The 26-year-old has played just three times in the last two years, after suffering with a series of injury problems.
Villa's win over Palace has moved them to within eight points of safety, with their next match coming against Leicester City.