"His potential as a player is very, very, high", he said.
"Callum needs to do it as well and take these opportunities when they come along".
After his hat-trick against Kiev last week, the World Cup victor was asked if he'd be willing to remain as one of Chelsea's rotation players due to his advancing age - to which he gave quite a strong response.
"We were able to score after five minutes. Making that step up is very hard and he showed that he can score goals from that position with his pace".
The Premier League giants are bidding for a first trophy under the Italian after losing last month's English League Cup final to Manchester City, and hoping to secure qualification for next season's Champions League.
Chelsea, winners of the Europa League in 2013, will fancy their chances of advancing, although they would be wise to beware a Slavia side who are top of the Czech league and knocked out Sevilla in the last 16.
How the draw for the Europa League quarter-finals panned out
"I am a competitor, I want to play every single game and to be happy on the pitch", he said.
The winners will face Benfica or Eintracht Frankfurt in the last four.
The Blues cruised past Dynamo Kiev 8-0 on aggregate after two legs and are into the quarter-finals of the competition.
"Chelsea are looking very, very good to go on and at least get to the final, if not win it", Walker added.
The first quarter-final will be played between Napolli and Arsenal.More news: Hamilton fastest in 1st practice at Australian GP