WASHINGTON (MarketWatch) -- San Francisco Fed President John Williams said that more bond buying could be needed if the economy faltered, according to a report. "If we really get a sustained, disinflationary forecast ... then I think moving back to additional asset purchases in a situation like that should be something we should seriously consider," Williams told Reuters. Williams said he's "worried" the European Central Bank response will be as timely and aggressive as needed. Williams told the publication he still expects the first rate hike in the middle of 2015. The Fed is expected to announce it will stop bond purchases at its October meetings.