The list of players who are opting out of the first major of 2020 continues to grow.

A total of 156 players will tee it up this week at TPC Harding Park in the first men's major championship since Shane Lowry left Royal Portrush with the claret jug 13 months ago. But the alternate list has gotten an extensive workout to keep the field full, with more than a dozen players withdrawing for various reasons.

That list includes 1991 winner John Daly, whose withdrawal was announced Sunday. Daly will miss the PGA for the first time since 2013, and he subsequently tweeted that the decision was based on safety concerns surrounding the COVID-19 pandemic:

A total of 14 players have now withdrawn from this week's event, including Ryan Moore who cited a "scheduling conflict." The various changes mean that Sweden's Alex Noren is now the first alternate.

Here's a look at some of the other players who have either withdrawn or opted not to accept their invite to this week's event at TPC Harding Park:

Ryan Moore (scheduling conflict)

Branden Grace (positive COVID-19 test)

John Daly (COVID-19 concerns)

Vijay Singh (injury)

J.B. Holmes (injury)

Charles Howell III (injury)

Paul Waring (injury)

Francesco Molinari (no reason given)

Padraig Harrington (COVID-19 concerns)

Y.E. Yang (no reason given)

Thomas Pieters (no reason given)

Shugo Imahira (no reason given)

Lee Westwood (COVID-19 concerns)

Eddie Pepperell (COVID-19 concerns)