Airlines that have been forced to rejig operations due to the grounding of the 737 Max could face a markedly different problem when Boeing Co.'s best-selling jet is finally cleared to re-enter service: a gradual switch to concerns about oversupply, a leading analyst warned on Monday.

The Chicago-based plane-maker has continued to produce the jet since it was grounded in March in the wake of two fatal accidents, and is expected to speed deliveries by 40 percent to 70 units a month when its factory doors reopen, in a bid to start clearing the backlog.

Rob Morris, global head of consultancy at U.K.-based Ascend by Cirium, said the combination of any rapid rebound in deliveries, economic worries and an accumulation of market pressures dating back before the crashes could make it hard to absorb the jets.