Rumours are circulating that, despite Mika Kallio's return to Pramac Ducati, Aleix Espargaro could continue with the team at Estoril - in place of Niccolo Canepa.

Espargaro thrived after being thrown in the MotoGP deep end, in place of Kallio, at Indianapolis and Misano.

Despite no prior knowledge of a MotoGP machine, the 20-year-old beat at least one rider in every track session at Indy - on his way to 13th in the race - then broke new ground with tenth (out of 17 riders) in Saturday morning free practice at Misano.

The Spaniard, whose best race finish in the lower grand prix classes is fourth position, then rode from 15th to eleventh in the San Marino Grand Prix - and stunned by setting the fifth fastest race lap.

Although Kallio is now moving back to the satellite team after substituting for Casey Stoner at Ducati Marlboro, Espargaro - who underwent an arm-pump operation straight after Misano - could remain in MotoGP for the final four rounds, albeit at Canepa's expense.

The Italian rookie, the youngest rider on the grid prior to Espargaro's arrival, came into the premier-class as a former FIM Superstock champion and Ducati test rider - but no experience as a 125 or 250GP rider.

The mechanical engineering student has done a solid, if unspectacular, job during his first 13 races, matching Kallio's best finish of eighth on the satellite bike (the Finn claimed seventh in his final factory appearance) and finishing all but the Indianapolis round, when he suffered a technical problem.

Unfortunately for Canepa, he was outpaced by Espargaro in every track session except warm-up (when Espargaro fell) at his home Misano circuit. Canepa also set a best race lap 0.775sec slower than his team-mate on his way to 13th out of 14 finishers.

GPone.com states that the rider switch 'seems certain' and that Espargaro 'has a plane ticket to Estoril'. However, Canepa's manager Carlo Pernat (also manager of Loris Capirossi) insists his rider has a contract until the end of the season, which he expects to be honoured.

Canepa is 16th in the world championship standings and the last of the full time riders. Kallio, who missed Laguna Seca, is 16 points and one place ahead of him. Both Canepa and Espargaro have been linked with a Moto2 ride for Pramac next season.

Pramac has so far been unable to confirm its Estoril rider line-up to Crash.net.