UPDATE: Arrieta has been cleared to start Opening Day.

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Chicago Cubs fans shouldn't be worried, but the recent issue with Jon Lester's bone chip should be kept in the back of one's mind, and now Jake Arrieta's availability for Opening Day also shouldn't be overlooked.

Arrieta left Thursday night's spring training game against the San Francisco Giants due to a blister on his thumb. Manager Joe Maddon said today that "blisters can be funny," while indicating an Opening Day start from Arrieta is no guarantee.

"Right now, we haven't called off the jam yet, but after another day or two, we'll look at it and then make our best determination at that point," Maddon added. "You don't want it to be chronic. They can become more chronic and you don't want that to happen.... [Being] the opening day starter always is prestigious. However, so is winning the World Series, and we definitely want to make the right call."

Arrieta threw only 34 pitches against the Giants and recorded just one out before he left the game. He surrendered five earned runs on four hits and two walks in the outing, and now the blister on his thumb may jeopardize his chances of starting on Opening Day. However, he insists it won't be a problem.

The blister is the least of Arrieta's worries at this point. The Cubs need to make sure the NL Cy Young winner is well-rested, considering he exceeded his career-high in innings pitched by 92 in 2015 (248 2/3 in 2015 vs. 156 2/3 in 2014). He admitted that he felt fatigue during the postseason, which may explain his final two outings (6.75 ERA on nine hits and four walks). He allowed 10 home runs in 229 innings during the regular season and then surrendered two in his final 10 2/3 innings of the postseason.

Arrieta said he expects to be ready for his final spring outing Tuesday and that his thumb is already healing well. While he thinks he'll be ready for Opening Day, Maddon said the right-hander still "needs to be stretched out" for the team for him to feel comfortable putting him on the mound to start the year. After all, he's thrown just 6 1/3 innings over three starts this spring.

While the Cubs are the favorites to win the World Series, there are certainly a number of questionable factors to keep in mind heading into the 2016 season.