Javier Hernandez left Manchester United because manager Louis van Gaal told him he had a "one percent chance" of playing as a striker if he stayed at the club, the Mexican has said.
Hernandez joined United in 2010, and scored 37 Premier League goals in 49 starts for the club. He was loaned out by Van Gaal to Real Madrid for the 2014-15 season.
The Mexico international joined Bayer Leverkusen for a reported 7.3 million pounds ($10.96 million) in August and has scored 10 goals in 11 league starts for the Bundesliga side and 18 in all competitions for the club this season.
United, in contrast, have struggled for goals, and their leading Premier League scorer is midfielder Juan Mata, who has just four in the league so far.
"Van Gaal said that I only had a one per cent chance of playing in my position, so I headed to Bayer," the striker told Spanish newspaper Marca.
"I felt confident from the very first day. I feel important, not just because of my goals, but because I feel that I'll start every game."
Hernandez joined United when Alex Ferguson was in charge, but saw his playing time dwindle after the Scot retired.
"I'm so grateful to Ferguson," he said. "I think he's the best there's ever been, especially his squad management skills.
"Every player had his place. A squad player could still play 15 games a season. He opened the door to Europe for me and I won two league titles there."