The 41-year-old former Barca and Spain midfielder has inspired the Catalan club to an impressive 13 trophies since he took charge in 2008, including three straight Spanish league titles and Champions League triumphs in 2009 and 2011.
However, elimination from Europe's elite club competition would be a fresh blow following Saturday's 2-1 La Liga reverse at home to Real Madrid which put their bitter Spanish rivals seven points clear at the top with four games left.
Real could get another crack at Barca in next month's Champions League final if they manage to get past Bayern Munich, who are seeking to protect a 2-1 lead from last week's first leg when they play at the Bernabeu on Wednesday.
The pacy Tello showed flashes of promise but wasted one of Barca's best chances with a wild effort, while Sanchez scored immediately after coming off the bench.
"If I had left other players out you would probably be asking me now why I did not include them," a defensive Guardiola told a post-match news conference.
"Maybe I did get it wrong," he added. "Maybe with Cesc or other players it would have gone better, who knows?"
Real coach Jose Mourinho, by contrast, executed a successful game plan that appeared to be modelled on the one his former club Chelsea used in last week's first leg at Stamford Bridge.
"In the end I have to take the consequences for my decisions and there is always a reason for those that I take," said Guardiola, who has yet to extend his contract beyond the end of this season, prompting speculation he could step aside.
"The adjective disappointing is not appropriate for what we did in London or here," he added.
"Disappointing is when your people do not perform. It's one thing to win or lose but disappointing is not the right word."
Didier Drogba, the scourge of Barca last week, is Chelsea's main injury doubt having missed Saturday's 0-0 draw at Arsenal with a knee injury.
