The Cubs’ pursuit of Japanese free agent Masahiro Tanaka could get very serious very fast, according to sources who say the business side of the operation already is boasting that the Cubs might land the top pitcher on the market. What puts Tanaka in play for the Cubs — who often are forced into mid-market decision-making because of debt-related restrictions — is that the often-exorbitant posting-bid price isn’t subject to restrictions on player spending that have been in place since the Ricketts family’s highly leveraged purchase in 2009, a source said. Tanaka, 25, could give the Cubs a front-line starter to build around as the homegrown hitting core comes together. General manager Jed Hoyer said last month that the Cubs planned to bid for Tanaka, a right-hander who went 24-0 with a 1.27 ERA for the Rakuten Golden Eagles in 2013. But some top Cubs baseball officials privately doubted they would be any more successful than they were in failed bids the last two winters for Yu Darvish and Hyun-jin Ryu, who went to the cash-flush Texas Rangers and Los Angeles Dodgers, respectively. Whether the Cubs get Tanaka could have a lot to do with the outcome of negotiations over this winter’s posting process — and at least a little to do with Jeff Samardzija. A proposal by Major League Baseball reportedly would cap posting bids in an effort to put more teams in play. The Rangers’ successful bid of $51.7 million two years ago was more than twice the Cubs’ second-place bid. Winning the posting process only earns the right to negotiate to sign the player to a big contract on top of that.