Perez won two of the four opening races of the 2023 season and, after his victory in the Azerbaijan GP, he was just six points behind Verstappen and touted as a potential title challenger.
The gap was extended when the Dutchman led a Red Bull one-two in Miami. Perez then had a disastrous weekend in Monaco, crashing in Q1 and finishing well out of the points after a fraught race.
Perez again had a scrappy qualifying in Spain that saw him start only 11th. He was able to recover to fourth place in the race.
Verstappen won both the Monaco and Spanish events, further extending his lead, with the gap between the Red Bull drivers now standing at 53 points.
Horner says that with a title challenge currently looking less realistic a solid race in Barcelona will help Perez to relax.
"I think for him that'll give him a lot of confidence coming out of this," he said. "He has had a difficult Monaco, difficult Saturday here, a stronger Sunday.
"And I think that looking at the gap now between the two drivers, which is pretty significant, in many respects that will take pressure off his shoulders, and I think that'll allow him just to now relax, not put pressure on himself and just re-find the form that he had in those early races."
He added: "I think that we know what Checo is capable of. We've seen in races like Azerbaijan and Saudi already this year, what he's capable of doing. And I'm sure he'll re-find that form in the near future."
The team's simulations had predicted that Perez could climb from 11th to fifth in Spain, and thus he exceeded expectations.
"The sim said on a clean race P5," said Horner. "He did one better than that in P4. We felt maybe the Ferrari would have better race pace than it had.
"He was getting within a couple of seconds of the podium as well at the end there, and hunting down George [Russell]. It was a very good recovery, particularly the second half of the race, for Checo."
