Arsene Wenger’s side suffered a 2-0 defeat by the Champions League holders in the first leg of their last-16 clash at the Emirates Stadium on Tuesday night.
Lionel Messi made the breakthrough after he combined with Neymar and Luis Suarez before the Argentina international finished from close range.
Arsenal substitute Mathieu Flamini conceded an 83rd-minute penalty within 60 seconds of his introduction as Messi doubled Barcelona’s lead.
And Bellerin, who started his youth career at the Catalan side but never played for the senior team before his move to Arsenal, posted a motivational message on Instagram on Thursday afternoon.
Bellerin wrote: “Disappointing result on Tuesday night, but we must continue to work hard for the 2nd leg! Now to UTD on Sunday #COYG”
Arsenal are in third place in the Premier League table and two points behind leaders Leicester City.
The Gunners were 2-1 winners against the Foxes in their most-recent Premier League game.
MORE: Latest Man Utd news
MORE: Latest Arsenal news
MORE: The latest football news