United announced on Thursday that Valdes, a six-time Primera Division winner, is being allowed to use the club's training facilities as he bids to return from the anterior cruciate ligament injury that has kept him out since March.
The 32-year-old, who is a free agent after leavingBarcelona this summer, will join in with first-team training once he has recovered from the injury.
When asked whether he would consider signing the Spaniard if he returns to full fitness, Van Gaal gave a cryptic hint that it might be a possibility.
"Manchester United has always their eyes open," the United manager said at his pre-match press conference on Friday.
Van Gaal handed Valdes his Barcelona debut in 2002 during his second spell in charge of the Catalan giants.
Valdes had been linked with a move to Liverpool, whose first-choice goalkeeper Simon Mignolet has come under fire for some sub-par performances this term.The Spanish goalkeeper became Van Gaal's first choice and remained so until the Dutchman decided to leave the Nou Camp in the summer.
But Van Gaal, whose goalkeeping coach Frans Hoek also worked with Valdes at Barcelona, was happy to give the three-time Champions League winner the opportunity to recover from the injury at United's state of the art training ground in Carrington.
"For me it's not a surprise (decision) because I have done it already with a lot of players," he said. "I have a relationship with a lot of players. I gave Ronald de Boer or Edgar Davids rehabilitation possibility or training possibility when they needed that, so he is one of these players.
"Robin van Persie also when he played for me in the Dutch squad last year, I allowed him to come to our medical department to get him fit for the World Championship (World Cup).
"I have always done that, and not only with big players but ones you've never heard of."
Valdes' compatriot David de Gea has enjoyed an outstanding couple of seasons as United's number one, but currently faces little competition for his first-team spot.
Anders Lindegaard looked set to leave Old Trafford in the summer, but he stayed to compete with Sam Johnstone and Ben Amos to be De Gea's backup.