The Manchester United star, who starts for Craig Levein's side in Vaduz, insists his side will do all they can to give themselves a chance of qualification prior to facing Spain
Craig Levein's side are currently in third spot in Group I although a win will move them above the Czech Republic with one game remaining.
Fletcher was initially ruled out of Saturday's clash in Vaduz although has overcome tonsillitis
to start the game and the Manchester United midfielder is determined to help put his side in a strong position prior to the trip to Alicante.
"This is a massive double-header," Fletcher said, speaking to BBC Sport. "A win against Liechtenstein is a must and we will do all we can to keep our hopes alive for Tuesday's match against Spain.
"These are two huge games and I was determined to be involved in both of them.
"I felt a lot better on Thursday and spoke to the manager about joining up.
"Obviously there is a lot at stake and everyone knows how passionate I am about playing for my country, so it wasn't a big decision to make once I started to feel better."
Levein, meanwhile, was full of praise for his skipper's determination to be involved for his country as they aim to secure a Euro 2012 play-off spot.
"It's a great boost to have Darren here, especially after losing Kenny," he said.
"He has a huge influence on the team and his presence alone will give the players a lift."