Craig Levein's side face Liechtenstein this evening before travelling to Alicante to play group leaders Spain on Tuesday.
The Manchester United midfielder had been ruled out of tonight's encounter with illness and was originally left at home.
However, Fletcher took a flight out from Manchester yesterday after recovering from his bout of tonsillitis.
"These are two huge games and I was determined to be involved in both of them," he said.
Levein is likely to be without striker Kenny Miller, who is expected to be replaced by Craig MacKail-Smith.