Movistar's Alejandro Valverde said the lay-off from a doping ban had affected Alberto Contador's rhythm and judgement, enough to hurt his chances of winning this year's Vuelta a Espana.
Contador (Saxo Bank-Tinkoff Bank) returned to competition earlier this month after being banned since February for testing positive for clenbuterol en route to winning the 2010 Tour de France, a title he was subsequently stripped of.
The 2008 Vuelta a Espana champion trails overall leader Joaquin Rodriguez (Katusha) by one minute in this year's edition to sit in third place. Contador is seven seconds behind Chris Froome (Sky) and the same time in front of fourth-placed Valverde.
"He's been laid off without competition for a while, so he is still trying to find his rhythm," said Valverde , the 2009 Vuelta champion. "He's third in the overall standings but we can all see he's a little nervous, attacking when he shouldn't be attacking. But I guess he has his plan and he's doing it for a reason."
Contador's ban also ruled him out of the Giro d'Italia and the London 2012 Olympic Games this year. The two-time Tour champion is one of only five riders to have won all of cycling's top three races during a career.
However, Igor Anton (Euskaltel-Euskadi) still thinks Contador should be considered a favourite to win the Vuelta.
"Contador may not be at his best but he looks like the one with the best chance of winning the Vuelta," said Anton, who is eighth overall. "He's got the most experience when it comes to any of these situations."
Contador, like Froome, will look to get through Tuesday's 10th stage with his gap to Rodriguez unchanged as Wednesday's time trial offers an opportunity to make up time on the race leader.
Valverde believes Froome is favourite in the time trial, even if he seems to be feeling the fatigue of a long season that included runner-up finishes at the Tour de France and Olympic Games (individual time trial).
"Froome is the most favoured for that day's time trial, but he still looked a little drained on the climb up Montjuic (to finish Sunday's ninth stage)," Valverde said. "He looked finished at the close yesterday, especially in the last 200 metres."
The 10th stage is a 190km leg in the western province of Galicia.