Christian Pulisic subbed out at halftime of USMNT World Cup opener after feeling tightness in calf

After a first half for the ages, USMNT fans got a scare when star Christian Pulisic did not return for the second half of the United States' World Cup opener against Paraguay.

The Hershey, Pennsylvania, native, who plays club soccer for AC Milan, assisted on the United States’ second goal, scored by Folarin Balogun, and was one of the team’s most noticeable players throughout the first half.

However, when the team emerged from the tunnel, it was revealed that Pulisic had been subbed out in favor of Sebastian Berhalter, son of former USMNT player and coach Gregg Berhalter.

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The thing was, the team did not give any reason for why the change was made.

It was reported during the FOX Sports broadcast that Pulisic had indicated to family in the stands that he was OK.

After the United States capped off its 4-1 victory, USMNT head coach Mauricio Pochettino shed light on why the star was substituted. Per The Athletic's Tom Bogert, Pochettino said Pulisic took a kick to the calf that caused some tightness, and the decision to remove him was purely precautionary.

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Some of the concern from fans stemmed from Pulisic's recent injury history. He sat out last summer's Gold Cup to rest after playing 50 club matches with AC Milan.

The following season, he dealt with several injuries. Most recently, according to ESPN, he missed a match last month because of a lower-back issue.

Pulisic is a key piece of the USMNT, and his absence was noticeable in the second half.

While Pochettino said the substitution was purely precautionary, American fans will likely remain uneasy until Pulisic is back on the field and fully healthy.