Robert Mathis has vowed to be back on the field by the Colts' season-opener in September, but team owner Jim Irsay said Monday the outside linebacker has yet to receive clearance from doctors to resume on-field activities as he recovers from a torn Achilles tendon.

Irsay told the Indianapolis Star that despite the uncertainty surrounding Mathis' return, the six-time Pro Bowler is progressing in his rehab.

"The good news is Robert is trending in the right direction," Irsay said, via the Star. "We're all very excited and pleased with the progress that he's making. The timetable is unknown. Will it be October 15? Will it be September 15? I really, at this point, no one knows."

More from FoxSports

The 34-year-old Mathis missed the first four games last season serving a suspension for violating the league's performance enhancing drug policy. He tore his Achilles last September, training for his return.

Irsay said the Colts are preaching patience with Mathis, who recorded 19.5 sacks in 2013.

"We just want to make sure that he's ready-ready when it's time to go," Irsay said. "He can come in, have a couple of years with us at this point in his career, and be the difference-maker he was.

"We're really excited about the prospect. Really, it's only been good news."

For his part, Mathis has been posting videos on Instagram highlighting his comeback.

(h/t Indianapolis Star)