The Rangers are becoming increasingly optimistic about their chances to sign Yu Darvish, a major-league source said Thursday.

The team has until 5 p.m. ET Wednesday to reach agreement with Darvish, after obtaining his negotiating rights last month. Darvish’s team, the Hokkaido Nippon-Ham Fighters, will collect the Rangers’ $51.7 million posting fee if the ace right-hander signs with Texas.

If the Rangers sign Darvish, it will probably signal that they are no longer pursuing free-agent first baseman Prince Fielder. One source with knowledge of the Rangers’ finances said this week that it’s unlikely the team can afford both players.

Darvish would return to the Fighters for the 2012 season if he fails to reach agreement with the Rangers. After the upcoming season, he would again be eligible to come to the major leagues via the posting system. But that scenario appears increasingly unlikely, as the Rangers’ confidence grows.

-- Jon Paul Morosi