Moses Kamara was left in tears after making the 3,000 mile (4,800 km) trip, only for the game to be cancelled.
He had been invited by friends at the Manchester United Supporters Trust to watch the Premier League match.
Now the group has offered to fund an extended stay for Mr Kamara.
Members offered to pay for a later return flight home, so he can watch the Red Devils' rearranged clash with Bournemouth on Tuesday.
And they are arranging a ticket for Moses to watch the team's FA Cup final against Crystal Palace at Wembley next week.
The fan, who works in security, said "he cried a lot" when the match was cancelled.
"I was so disappointed and I cried right away and people come around me and hug me," he said.
"I come far away from Sierra Leone. I come to watch this match and it doesn't happen."
"This is my first time in real life to watch Manchester live and it doesn't happen."
An "urgent" inquiry has been demanded after a dummy bomb used in a security exercise resulted in the 15:00 BST kick-off match being postponed.
Fans were evacuated and a controlled explosion was carried out on the device, which police said was accidentally left at the 75,000 capacity stadium.
Ian Stirling, vice chairman of MUST, said: "When we heard the game was abandoned we had to tell Moses and the poor lad was distraught - being so close to the ground and not being able to go in, not knowing when he might get this chance again.
"He's still distraught at not getting in to Old Trafford. That was his dream. But we're trying to do the right thing for a friend."
Manchester United said it was refunding all tickets for Sunday's game and allowing ticket holders from both clubs to watch Tuesday's re-arranged game for free.
A Manchester United fan from Sierra Leone whose dream trip to Old Trafford was ruined by Sunday's dummy bomb drama will attend the FA Cup final thanks to a campaign by supporters.