Hudson is scheduled to throw off a flat surface on Saturday and then follow that up with a bullpen session.
"Then we'll have a better idea when he comes back after that," Bell said on Thursday. "We'll have to wait and see what happens. It is really tough to say until we see him off the mound and how he feels the next day."
The Royals could backdate Hudson on the disabled list, so he would be eligible to be activated by April 8.
"If we need him available on the eighth and he can be available on the eighth, we can make that work," Bell said.
Hudson has made only two starts in Spring Training and was scratched from a Minor League start earlier this week with the shoulder tightness.
"His pitch count is only going to be up around 70-75, and we would prefer not to put somebody in the rotation that has that kind of a pitch-count limit," Bell said.
Hudson went 7-6 with a 5.12 ERA in 26 games, including 15 starts, last season with the Royals. He was slotted to be the No. 3 starter.
The Royals appear to be setting up Zack Greinke to start the third game of the season, but Bell would not confirm that.
"We have some idea, but it is not anything official yet," Bell said.
The Royals-Athletics game was called off in the top of the fourth with Kansas City up, 4-2, after the second rain delay.
Royals starter Jorge De La Rosa threw 55 pitches in three innings, allowing two runs on four hits, walked one and struck out two.
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"On kind of a really nasty day, I thought he did fine," Bell said. "We misplayed some balls in the outfield that got him into trouble, but he worked his way out of it. With De La Rosa, you would always like to see him be more efficient with his pitches, but overall I felt it was fine.
"We would have liked to see him get a full day in, but you can't fight Mother Nature. He got his work in and he didn't harm his chances of being in the rotation by any means. I think his stuff was probably as good as we've seen it all spring, so that's a good sign.
McClure had a similar assessment of De La Rosa.
"He did OK," McClure said. "I'd like to see his pitch count go down. I'm happy where he is moving to. I think he pitched very well for the conditions today. He was moving a little faster tempo-wise in his delivery. He's in the [rotation] picture."
Rearranging the pitching:
David Riske, Todd Wellemeyer, Jason Standridge and Ryan Braun were all scheduled to pitch an inning on Thursday, but were washed out with the rain.
Riske threw an inning in the cages once the Royals went back to their Surprise complex and is scheduled to throw an inning on Friday in a Minor League game. McClure said the other three would make the Friday trip to Tucson and pitch against the Diamondbacks.
Before the rain:
Alex Gordon went 2-for-2 with a double and scored two runs before the rain halted action.
Emil Brown also had two hits and an RBI, while Mike Sweeney had a double. In the fourth, Jason LaRue was hit by a pitch with the bases loaded and Andres Blanco walked with the bases loaded.
Ken Ray, who is trying to claim a bullpen vacancy, has been pitching much better lately.
"I started off slow, which is to be expected," Ray said. "Last year, I came into Spring Training ready to go after going to winter ball. I was kind of behind to start this spring. I took some time off from throwing and playing catch because I had a lot of appearances last year. I needed the rest and the break. It is finally catching up to where I need to be."
Bell said he would open the season with seven relievers.
"There's still a spot or two open," Bell said. "We feel pretty confident that the guys we keep will throw strikes and that is what we're looking for."
Gil Meche will start on Friday against the Diamondbacks at Tucson Electric Park in a 3:05 p.m. CT start.