After limited chances under Xabi's predecessor, Carlo Ancelotti, the Turkey midfielder has been leaned on heavily by Real's new coach.
Guler told L'Equipe: "I have complete faith in Xabi Alonso's plans. If one day he tells me to play in goal, I'll buy gloves!"
The 20-year-old was also asked about French teammate Kylian Mbappe.
He added: "Mbappé's qualities and mine are made for each other.
"We understand each other really well; everything flows. Sometimes, we chat a bit before matches: 'Today we should do this, that.' There are also nights when a look is enough."