The Netherlands international has made just 10 Bundesliga appearances in 2015-16 due to ongoing injury problems, with Douglas Costa and Kingsley Coman impressing on the wings in Robben's absence.
Some have even suggested Bayern might be better off without the 32-year-old, but Guardiola has jumped to the defence of the Dutchman.
"Arjen needs time to get back to his best. But he is hugely important for me with his desire to get forward and his strength in one-on-ones," he told reporters.
"He was hardly ever injured during my first two seasons in charge and he is still a key player for me."
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Guardiola also insists that he has no problem with Carlo Ancelotti visiting Munich to meet club officials as he prepares to take the reigns at Allianz Arena when the Catalan departs for Manchester City.
"I did not meet Ancelotti," he added.
"I was in Bochum for the DFB-Pokal game and was with my family after the match.
"But it is only normal that he paid a visit to Munich. That is not a problem for me at all."
Bayern take on Augsburg on Sunday and Guardiola has revealed Mario Gotze could make his return after a lengthy spell on the sidelines due to an adductor injury, while Serdar Tasci is in line to make his official debut for the Bavarians.
"I am not sure yet whether Gotze and Tasci will be ready for Sunday," he added.
"The players have a day off on Friday and will then be training on Saturday. We will make a decision after Saturday's training."