Knowing how hot it is supposed to be on Sunday, head coach Kyle Shanahan said the San Francisco 49ers wanted to wear their all-white uniforms for Week 5 against the Arizona Cardinals, but they found out by the league that was something that needed to be decided before the season started, so it couldn’t get approved.

The Niners will wear their throwbacks with white pants in Week 5. Here’s Shanahan’s explanation about the uniforms:

“We got the memo earlier in the week that it was going to be hot like this. So we asked on Monday, and we weren’t allowed to do it. We had to do it before the season started. In order for us to do it, we had to make a commitment before the year that we wear all-whites until the middle of October or whatever and then go to normal.

But it’s not usually this hot, so we’ll probably do that moving forward. They’ll let us do our throwbacks, just alternate it with others. We’ll get as much white on as possible. The most we can possibly do is white pants.”

Shanahan said the team had never known in advance how hot it would be, and since his time in the Bay Area, it never felt too hot, even on the hottest days; he said he still needs a hoodie. But this week has been different, and he believes that’ll be the case on Sunday, which is why the team looked into it.

He said it’s been a rule for “a little bit,” and the team just needed to be reminded about it.

Shanahan expects more players to get pre-game I.V.s:

“I would assume so. Each person is different. Sometimes, when you push I.V.’s a lot, people think they don’t have to hydrate at all. But it depends on the I.V. So, we’re not preaching all of that yet. That’s usually what you do in these situations.

A number of guys, that’s usually what they do anyway in these situations. I wouldn’t be surprised if a lot more are doing it this Sunday.”

Shanahan went to the University of Texas. He said he “always” took I.V.s before a game. When asked how it made him feel, Kyle was pretty adamant: “Better. Better. I still do it. If I had too much fun the night before.”

The thought behind getting as much white on the uniforms is for hydration purposes, according to Shanahan. Per Accuweather, temperatures are expected to be around 97 degrees at kickoff.