The Albion made an attempt to secure Cole Palmer from Manchester City in the summer.
However, the English winger instead opted for Stamford Bridge and has become a key player.
"We tried to bring him in the transfer market last summer. We thought he could be a top player," De Zerbi told a news conference.
"The qualities of Palmer are clear for everybody, but not when he played for Manchester City. This season he is playing very well, he is scoring a lot of goals."
"The quality of Palmer is very high," he added, as his team prepare to take on Chelsea in midweek.
"He's a problem for us tomorrow because he can start in the winger position and come inside or (play as) a number 10 as well."