The Spanish goalkeeper has been training with the Red Devils this week as he seeks a new club after leaving Barcelona at the end of last season.
Valdes is recovering from a serious knee injury he suffered prior to his Camp Nou exit but that does not mean United are not monitoring him closely.
"Manchester United always has its eyes open," said van Gaal when quizzed on the possibility of signing Valdes.
32-year old Valdes trained with Liverpool recently but was not offered a contract by the Anfield side.
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