Woolworths Group Ltd (ASX: WOW) shares are inching higher today.

Shares in the S&P/ASX 200 Index (ASX: XJO) supermarket giant closed yesterday trading for $28.14. In morning trade on Wednesday, shares are changing hands for $28.15 apiece, up 0.04%.

For some context, the ASX 200 is down 0.6% at this same time, following the lead of the S&P 500 Index (SP: .INX), which closed down 1.1% overnight amid ongoing tariff concerns.

Taking a step back, Woolworths shares are down 12.2% in 12 months. That compares to a 1.4% gain by the ASX 200 and a 12.1% gain by rival Coles Group Ltd (ASX: COL).

After that big year of underperformance, Macquarie analysts point out that Woolworths stock is now trading near a five-year low valuation relative to Coles shares (courtesy of The Nightly).

The analysts said this is mostly due to negative investor sentiment surrounding the pending Australian Competition and Consumer Commission (ACCC) inquiry report.

But it's the delivery of that report, expected in the coming weeks, that could offer a boost to Woolworths shares as well as Coles shares.

Why Macquarie is bullish on Woolworths shares

Macquarie raised Woolworths shares to an outperform rating. The broker left its price target unchanged at $30.80 a share. That represents a potential upside of 9.4% from today's levels.

Woolworths stock also trades on a fully franked dividend yield of 4.8%.

The analysts said that following the release of the ACCC report into the supermarket sector, investors are likely to buy Woolworths and Coles stock. They pointed to similar moves in the past that followed the release of regulatory reports into the big ASX 200 bank stocks, childcare, and Qantas Airways Ltd (ASX: QAN).

Macquarie said its analysis indicates "the market tends to 'sell the rumour' and 'buy the fact'".

According to the analysts (quoted by The Nightly):

100 days prior to the final reports being released, these groups on average delivered a one per cent fall in return. However, upon conclusion or release of the final report, there is a significant turnaround in performance.

Macquarie said the impacted groups previously returned an average of 17% upon the conclusion of the reports into their industries.

"This is particularly true for Woolworths, which is currently trading at close to a five-year low relative valuation (compared with Coles)," the analysts said. "We believe largely driven by negative sentiment as a result of press and ACCC focus."

Atop its upgrade of Woolworths shares, Macquarie also reiterated its outperform rating on Coles shares.

The broker said it is increasing its exposure to defensive stocks like Woolworths and Coles amid concerns over the global growth outlook.