City drew 2-2 with Arsenal last weekend, dropping two points that meant the Champions League fate was out of the Blues’ hands.
But the Hammers’ 3-2 win over United means City now need just a point away to Swansea to ensure a top four finish.
“In the Premier League, everything can happen and everything is unpredictable,” said Ferna.
“I was hoping West Ham could beat United and I’m glad they actually did and now our fate is back in our hands - so we must win our final game against Swansea.
“We didn’t beat Arsenal but we now have a chance to complete the task we set out to achieve last Sunday.
“Swansea are a very tough team to play and the last two seasons we have gone to The Liberty Stadium, we’ve had two very hard games.
“I’m sure they’ll want to prove something, not only because they are playing in front of their own supporters for the last time this season, but with their manager signing on for two more years, the Swansea players will want to prove they are worthy of a place in his squad next season.
“We need to be 100% focused in order to win and play at our top level.
“I’ve only played there twice before, but it’s a ground I always enjoy playing at. It’s been enjoyable for me because we’ve won both times and I got a goal in 2014, but it’s a nice stadium, the pitch is excellent and there is always a great atmosphere.
“I hope I come away this Sunday feeling as happy as I have done on the last two visits.”
One of the candidates for City’s Player of the Season, Ferna added: “I’m very happy with the way I’ve played this season – last year I didn’t play as many games as I would have liked or had been used to before I signed for City.
“This year was different and I played a lot more and played the way I like to play and I know I’m capable of, so on a personal level, I’m very happy with my own contribution.
“As a group, we didn’t reach the objectives we set out to achieve so that is disappointing but we can still end the season on a high note this Sunday.”
