FRANKFURT (Reuters) -Deutsche Bank is expected to post a loss for the second quarter, according to a consensus forecast published on Monday, as a protracted investor lawsuit over its Postbank division threatens to erode earnings.

Any loss at Germany's largest lender would break a streak of 15 consecutive quarters in the black in a setback for the bank's turnaround under CEO Christian Sewing.

The bank has warned profit would take a hit in the quarter because it would book 1.3 billion euros ($1.42 billion) for the long-running lawsuit claiming it underpaid for its purchase of its giant Postbank division.

The bank, which has strongly disputed the claims, declined to comment on the analyst forecasts posted on its own website.

Deutsche publishes its earnings on July 24. The bank's actual results have exceeded analysts' expectations in recent quarters.

The new consensus forecast does show each of the bank's four key operating divisions posting profit before tax.

But the post-tax bottom-line loss attributable to shareholders could be around 280 million euros in the quarter, according to Reuters calculations based on the consensus.

That is wider than a 170 million loss foreseen in the bank's previous consensus forecast dated in May, and compares with a reported profit of 763 million euros in the second quarter of last year.

The bank's management launched an overhaul in 2019 to restore profit after years of hefty losses.

Many analysts and investors have praised the bank's leaders for improved earnings but have criticised the bank for a drumbeat of regulatory and reputational issues.

Postbank, the no-frills lender that Deutsche bought during the financial crisis, has become a source of consumer complaints and regulatory scrutiny.

But Deutsche has made progress on some outstanding problems.

On Friday, Deutsche confirmed that it had settled for an undisclosed sum a 500 million euro lawsuit with a Spanish hotel company that claimed losses on derivatives products.

The company, Palladium Hotel Group, did not reply to a request for comment.

($1 = 0.9171 euros)