Borthwick is away with England this weekend, but Barkley starts at stand-off at Guinness Premiership bottom club Leeds on Sunday.
"I am positive that Olly's efforts and commitment will continue until he departs," said Meehan, whose side went into the weekend third in the table.
"However, I am surprised when you consider how far the team has come in the last 18 months, the style of rugby we are playing and how involved he has been in its evolution."
Barkley is the second highest points scorer in Bath's history with 1,538 points from 164 appearances. He has also been capped 21 times by England, although England coach Brian Ashton has not included him in his current Six Nations squad.
"This was not an easy decision to make and I am determined to leave the club on a high at the end of the season," said the 26-year-old.
"We are challenging strongly in the Premiership and hopefully we can bring some silverware back to the Rec."
In addition to Borthwick Bath, beaten at home by Wasps last weekend, are without prop Matt Stevens, hooker Lee Mears and flanker Michael Lipman, but they will still be expected to record a comfortable victory over Leeds, who have only one league win to their name and are in a fight with Worcester to avoid relegation.
The final game of the weekend sees sixth-placed Harlequins visit fourth-placed Saracens.
The gap between the two narrowed when Quins defeated Worcester last Saturday and Saracens lost at Newcastle.
Tom Guest replacing England number eight Nick Easter is the only change made by Dean Richards - that means Danny Care again plays at scrum-half rather than axed England number nine Andy Gomarsall - while for Saracens back row star Richard Hill and full-back Brent Russell are welcomed back, but centre Andy Farrell is injured.
Alan Gaffney, the home side's Director of Rugby, commented: "The players have reacted well this week. I still believe we are playing some pretty good rugby, but we need to set the bar even higher now.
"We've not been accurate enough in terms of our execution. We've been creating a number of opportunities in games, but we're just not putting them away and that's something we've focused on."