Johnson just recently returned to action following a six-week injury lay-off.
He said: “Everyone says the title is done for us but two defeats for United or Arsenal and a couple of wins for us or Chelsea and it is right back on.”
Johnson added: “The Champions League is massive and the competition at the top is getting tighter and tighter.
“All the fans are excited about the semi-final, I’m excited about the semi-final, the nation is as it’s a massive game, but it’s important we focus on the big games coming up in the Premier League.
“Any time you go to Stamford Bridge, it is tough. We won 4-2 there last season, we played them off the park and, hopefully, we can do the same this year.
“But nobody is safe for a Champions League spot and Chelsea are still a top, top team.”
