The 42-year-old opted not to play at the Texas Open last week and has struggled to play his way into contention during any of the tournaments in which he has featured this year.
"I'm a little bit nervous heading in because I didn't compete the week before as I have for many years in the past," he told reporters.
"I want to play well in this tournament. I love this tournament so much and I'm nervous because I haven't been in contention since the Sunday of the Houston Open, and that's 10 or 11 days as opposed to three.
"That's what I'm nervous about, being mentally tuned in for those opening five or six holes. It's always a challenge when you haven't been in contention to be really mentally focused and sharp."
Mickelson has only finished out of the top 10 twice from his last 14 outings at The Masters.