The statement says: "Reports in Tuesday's press claimed the Reds defender has experienced a recurrence of an old groin injury and would miss the key Premier League clash.
"However, the influential 28-year-old centre-back trained with the rest of the squad at Carrington on Tuesday, and is considered fully fit and ready to play against the Gunners."
Rio hopes to get a good result at the Emirates but thinks United should be thinking more about consistency than just winning the 'big' games.
"We're scoring goals and it's a big difference from the start of the season. We were creating chances but weren't converting them.
"Now we seem to be putting them in the back of the net and that bodes well.
"It's looking good but now it's got to continue. We have to sustain it over a good amount of time. This is just the start.
"Hopefully we'll be saying this after the Christmas period and we can say we've got a consistent strike force and a consistent team."