Chipotle Mexican Grill Inc.'s (CMG) stock has had a nice run so far this year, but Morgan Stanley sees room for even more upside, lifting its rating on the stock to overweight from in-line and upping its price target.

In a research report, Morgan Stanley analyst John Glass pointed to the fast-food chain operator’s turnaround as a reason for his optimism. "CMG is still early into a sales turnaround and has an attractive management change narrative and earnings recovery story," wrote Glass in a note to clients covered by CNBC.  He said a change in management and an incentive plan that is designed to boost earnings, lots of “low hanging” opportunities in marketing, product development and operational initiatives and less competition, should bode well for the turnaround and thus the stock. The analyst set a $600 price target on the stock, implying shares can gain an additional more than 20%. So far in 2018 Chipotle stock is up 60%.  (See also: Chipotle's Hungry Investors May Boost Stock 20%.)

New CEO Breeds Optimism

Earlier this year Chipotle appointed Brian Niccol as chief executive. He came from Taco Bell where he had a track record of boosting the business. The appointment was greeted with optimism on the part of Wall Street analysts. In a CNBC interview in March the new CEO said the immediate task at hand was reminding consumers why they love Chipotle. "I think there [are] opportunities to use what we have and present it in new forms, new varieties, to get people re-engaged with what they love about Chipotle," he said at the time. (See more: Chipotle: New Leadership Fuels Turnaround Optimism.)

Easy Money Days Over

Still, despite Morgan Stanley's optimism, not every investor is in the bull camp when it comes to the company. During a segment on CNBC “Trading Nation” last week, Matt Maley, a strategist with Miller Tabak, warned the days of a surging Chipotle stock could be coming to a close. The reason: Shorts are no longer betting shares will decline. "The short interest on the stock has come down dramatically over the last six to nine months," Maley said during the appearance. He said investors weren’t going to see the stock move as shorts rush to cover their positions. According to CNBC, Chipotle's short interest stands at 9.5% of its overall float, which is down from 13.5% at the end of last year. CNBC noted that in 2006, Chipotle had short interest of as much as 40%. If the stock rises, shorts may be forced to cover their bets, which drives the share price higher as they buy shares to pay back the stock they borrowed. “I think the easy money has been made and I'd be a little bit careful on this one," said Maley.